Re: Why two fuses for a 5 ton residential AC?
Lloyd E. Sponenburgh
news:fbkm55d58bdd5l29i...@4ax.com:
> Does anybody know why a 5 ton residential air conditioning
compressor
> needs to have a 50 amp circuit breaker at the meter box and then a
second
> set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>
> Those 60 amp fuses seem to be a duplication IMHO and are a pain to
change
> periodically.
In most areas, the fuses are redundant. The important part is that
there be a manual disconnect visible from the unit (for safety in
servicing). Those same disconnects are available fused or not fused,
and it may be your electrician just had that one available.
LLoyd
David Lesher
>Does anybody know why a 5 ton residential air conditioning compressor
>needs to have a 50 amp circuit breaker at the meter box and then a second
>set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>Those 60 amp fuses seem to be a duplication IMHO and are a pain to change
>periodically.
A positive disconnect at (or "in direct view" maybe) the rotating machine
is required by many/most codes.... and a hell of a good idea.
Many older ones had fuses. If the breakers are correctly sized for the
wiring & AC unit; I'm not aware of any reason for more fuses. Maybe the
main panel was upgraded at some point.
Replace the disconnect with an unfused one.
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Jim Stewart
> nom...@noplace.org writes:
>
>> Does anybody know why a 5 ton residential air conditioning compressor
>> needs to have a 50 amp circuit breaker at the meter box and then a second
>> set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>
>> Those 60 amp fuses seem to be a duplication IMHO and are a pain to change
>> periodically.
>
> A positive disconnect at (or "in direct view" maybe) the rotating machine
> is required by many/most codes.... and a hell of a good idea.
>
> Many older ones had fuses. If the breakers are correctly sized for the
> wiring & AC unit; I'm not aware of any reason for more fuses. Maybe the
> main panel was upgraded at some point.
>
> Replace the disconnect with an unfused one.
Before going to all that work, you might
try cutting power to the box and carefully
cleaning and tightening the fuseholders.
Make them and the fuses shiny with fine
sandpaper. A poor connection can generate
enough heat to blow the fuse even though
the fuse rating hasn't been exceeded.
Proctologically Violated��
<nom...@noplace.org> wrote in message
news:dmpm55tvn8chamnkv...@4ax.com...
> On Mon, 13 Jul 2009 16:37:12 +0000 (UTC), David Lesher <wb8...@panix.com>
> wrote:
>
>>nom...@noplace.org writes:
>>
>>>Does anybody know why a 5 ton residential air conditioning compressor
>>>needs to have a 50 amp circuit breaker at the meter box and then a second
>>>set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>>
>>>Those 60 amp fuses seem to be a duplication IMHO and are a pain to change
>>>periodically.
>>
>>A positive disconnect at (or "in direct view" maybe) the rotating machine
>>is required by many/most codes.... and a hell of a good idea.
>>
>>Many older ones had fuses. If the breakers are correctly sized for the
>>wiring & AC unit; I'm not aware of any reason for more fuses. Maybe the
>>main panel was upgraded at some point.
>>
>>Replace the disconnect with an unfused one.
>
>
>
> Uniform Electrical Code and UBC.
>
> I'm sure the cable is adequate gauge. It is about 50 feet run. What size
> would be minimal? Best?
My 5-ton unit draws 19 amps per leg.
So, in principle, #10 wire, or in some places, even #12 wire, would
theoretically suffice.
Proly #8 would make most people feel better.
And, of course, the wire needs to be sized to the breaker.
I've had compressors in that same unit draw **40 A** per leg....
goodgawd.....
Why are you having to replace a 60 A fuse, which is in series with a 50A
breaker?
Is it overheating, as per Jim?
I wouldn't do aluminum foil. Use a copper rod.
But, if the fuse is overheating, a copper rod could overheat as well.
--
Mr. PV'd
Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
glad to see me??
Experiment on Homo Sapiens -- CEOs, Lawyers, and Politicians, in
particular.
Spare the animals.
Click here every day to feed an animal that needs you today.
www.theanimalrescuesite.com/
>
> To replace the disconnect with an unfused one would involve the power
> company radio-disconnect box (for economy summer rates).
>
> Would wrapping the old fuse with tin foil work? A small copper plate
> would be nicer - don't think I have any. How about a piece of tin from a
> can?
>
> The positive disconnect - changing box is clearly an 'unattractive' idea.
> I understand the reason for it.
> In case of a fire - could an insurance claim be denied because of altering
> unneeded fuses?
>
> Mike
jeff_wisnia
In my case the fuse clips were ok, it was the switch contacts which got
grotty with age, developed a bit too much resistance and the heat from
the current flowing through that resistance got conducted through the
nearby fuse clip and fried the fuses, usually opening the circuit by
melting the solder joining the fuse link to the inside of an end cap and
thoroughly charring the fibre fuse body so the fuse fell apart when I
went to pul it out of the clips.
That kept happening in a fused disconnect n atticin the attic feeding
our second floor heat pump, where high currents flowed when the
auxillary resistance heaters kicked on.
I'd clean everything up real nice, smear KoprShield on contacting
surfaces and still a fuse would crap out a year or so later.
I changed out the entire fused disconnect and things were ok for 2-3
years and the same shite started again.
That's when I threw out the fused disconnect and replaced it with an
unfused "pull out" disconnect. Haven't had any trouble with it in years.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.
Jim Stewart
> I take that to be 6 ga. and very adequate.
>
> This 'cleaning and tightening the fuse holders' was my original problem -
> years ago. My last fuse has lasted years. I still like to be rid of the
> fuses that appear to not be needed.
>
> Would a thin wall 3/4inch OD piece of copper tubing be able to carry the
> current?
> How about a piece of 1/2inch (3/4"OD) galv iron pipe (my personal
> preference-grin) or do I really need the 3/4inch copper rod?
That might work fine until an inspector or
a real electrician opened the box and unleashed
a shitstorm... I wouldn't do it.
David Lesher
>>Replace the disconnect with an unfused one.
>To replace the disconnect with an unfused one would involve the power
>company radio-disconnect box (for economy summer rates).
Why? Do they lock the disconnect?
>Would wrapping the old fuse with tin foil work? A small copper plate
>would be nicer - don't think I have any. How about a piece of tin from
>a can?
Steel pipe would be really bad idea, ditto foil. I'd SWAG that thickwall
copper pipe would work but by them, you'd have been better to replace the
disconnect.
John Husvar
Howsomever--insurance companies seeming to be looking for _any_ excuse
not to pay off on a claim, I'd play safe and continue replacing the
fuses or replace he whole disconnect with a commercial UL listed one.
Cheap insurance insurance.
David41616
as the supply? Usually those fittings have room for two wires in the
screw terminal.
Dave
rangerssuck
> I take that to be 6 ga. and very adequate.
>
> This 'cleaning and tightening the fuse holders' was my original problem -
> years ago. My last fuse has lasted years. I still like to be rid of the
> fuses that appear to not be needed.
>
> Would a thin wall 3/4inch OD piece of copper tubing be able to carry the
> current?
> How about a piece of 1/2inch (3/4"OD) galv iron pipe (my personal
> preference-grin) or do I really need the 3/4inch copper rod?
>
Are you really hellbent on having a war with your insurance company?
Remember, they're in the business of collecting premiums, not paying
claims. Even though you & I both know that the pipe will carry the
current, it's not UL approved, and the insurer is sure to use it as an
excuse not to pay.
Reall, changing the box should be pretty simple, especially if you can
just get the same model without the fuse holders. Just turn off the
breaker at the main panel, and you're looking at waht, four wire
connections and two pipe connections?
Just sayin' is all.
Andrew VK3BFA
<UNfit...@UNoptonline.net> wrote:
> <nom...@noplace.org> wrote in message
>
>
> Why are you having to replace a 60 A fuse, which is in series with a 50A
> breaker?
> Is it overheating, as per Jim?
>
> I wouldn't do aluminum foil. Use a copper rod.
> But, if the fuse is overheating, a copper rod could overheat as well.
>
>
Hey PV - its a troll. Feeding into peoples knowledge to keep em going
- as you say, how come the circuit breaker doesnt trip first - their
usually faster than slo-blo fuses. And for all the rest of his post -
well, theres a limit to how far you can go with a troll.
Andrew VK3BFA
Larry Jaques
<wb8...@panix.com> scrawled the following:
>nom...@noplace.org writes:
>
>>Does anybody know why a 5 ton residential air conditioning compressor
>>needs to have a 50 amp circuit breaker at the meter box and then a second
>>set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>
>>Those 60 amp fuses seem to be a duplication IMHO and are a pain to change
>>periodically.
>
>A positive disconnect at (or "in direct view" maybe) the rotating machine
>is required by many/most codes.... and a hell of a good idea.
>
>Many older ones had fuses. If the breakers are correctly sized for the
>wiring & AC unit; I'm not aware of any reason for more fuses. Maybe the
>main panel was upgraded at some point.
Maybe that's what the guy/electrician had in the truck at the time.
>Replace the disconnect with an unfused one.
Right. The one I put in (saving myself $450 from the cost of the
installation) was a simple disconnect. I installed the run for the
condenser, the main unit, and the lights in the attic. Total: about
$95, including the 250' spool of 12/3 romex, 30' of 10/3 romex, the
disconnect, three lamp sockets, breakers for those, plus breakers and
L6-20 sockets/plugs for three 240v circuits for the gar^H^H^Hshop. Oh,
add 50' of 12/3 cord in that price for the bandsaw and dust collector.
--
Mistrust the man who finds everything good, the man who finds everything
evil, and still more the man who is indifferent to everything.
-- Johann K. Lavater
Larry Jaques
<jste...@jkmicro.com> scrawled the following:
Erm, wouldn't the added resistance drop the voltage, resulting in the
circuit exceed the current limits, Jim? Just a thought.
Is it heat, current, or are both considered the norm in a corrupted
connection?
Bob AZ
> Does anybody know why a 5 ton residential air conditioning compressor
> needs to have a 50 amp circuit breaker at the meter box and then a second
> set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>
> Those 60 amp fuses seem to be a duplication IMHO and are a pain to change
> periodically.
>
> Mike
Mike
Must be Air Conditioning season again.
So the first thing to realize is the difference in the functions of
the breaker and the fuses you seem to have. The 50amp breaker is to
protect the wire from the breaker panel to the AC unit itself. Or in
your case the disconnect. The disconnect happens to be fused. Not
uncommon. Perhaps this is all the installer had. There does need to be
a disconnect in view of the AC unit. Dafety thing. Fused or not.
The breaker does need to be sized according to the capacity of the
wire. A 50 amp breaker is not the correct size for #10 wire. #10 wire
is usually rated at 30 amp but there is a safety factor of 20% so the
maximun continuous load should not be over 24 amps. And breakers
should not be oversized. If they are the breaker will not trip when
the wire is overloaded. And there are breakers and breakers. Some
breakers are for motors and their usually high starting currents. A
good electrician should be able to straighten this situation out.
Now for the fuses. As with breaker there are fuses and fuses. Are you
using the proper type of fuse? From you posting it seems to me that
you need the lag type of fuse. There are several different types.
Voltage ratings for fuses are important also. The installation
literature for the AC unit should specify what type of fuse in the
disconnect or possibility specify no fusing is needed. And fuses do
get tired. But certainly not yearly. Usually fuses with AC units
connected fail because the compresser or condenser fan motors are
getting tired. Start to overheat and internal wear. Or a big one is
dirty coils. Both condenser and evaporator. Have you checked the motor
amps lately? Still in spec with the original readings taken during
installation? 60 amp lag fuses should be large for a 5 ton.
Particularly the newer higher SEER units. Mine are 30 amp but my SEER
rating is 19. Again a service call from a real AC man should get to
the heart of the fuse problem.
Don't as some suggested cheat or short out the fuse block. This is
asking to die or burn or both.
Hope this helps.
Bob AZ
Andrew VK3BFA
> Not so - I let idiots (apparently) install this many years ago.
> Finally got some answers.
>
> Why the 50amp does not trip first - it is clearly not a perfect world.
> M
>
> >Hey PV - its a troll. Feeding into peoples knowledge to keep em going
> >- as you say, how come the circuit breaker doesnt trip first - their
> >usually faster than slo-blo fuses. And for all the rest of his post -
> >well, theres a limit to how far you can go with a troll.
>
> >Andrew VK3BFA
Well, taking you at face value, and assuming you have some electrical
knowledge......
1.Check that the fuses are indeed slow blow.
2.Check that the circuit breaker is indeed 50 amps - and is working.
if they are as you state, the laws of physics dont apply in your
particular case....
Corrosion/wear and tear/loose contacts in the fuse unit - could be -
weirder things have happened - does the thing blow at switch on? (it
shouldn't, slo-blo fuses are designed to handle starting loads) -
stick your hand on the box, does it get warm, ditto the switch, then
check it out as described by others.
And even thinking of replacing fuses with foil/copper rods etc is
absolutely insane, hence my comment you were a troll - its what you
would expect in the 3rd world, not where you live. The mind boggles at
even thinking of doing such a grossly unsafe thing.
Otherwise, if nothing works, a prayer to whatever god you worship is
your only option.....(or pay an electrician to check it out)
Andrew VK3BFA
jk
>- as you say, how come the circuit breaker doesnt trip first - their
>usually faster than slo-blo fuses. And for all the rest of his post -
>well, theres a limit to how far you can go with a troll.
>
>Andrew VK3BFA
Regardless, the fuse sustains some minor damage each time the current
exceeds its rated current, the CB does not. It might take the CB
60-1000 seconds to open for overloads, in that time a fair amount of
damage can occur to the fuse, without yet clearing it. As this
happens start after start, eventually the fuse fails, without tripping
the breaker.
jk
Bruce L. Bergman
>Does anybody know why a 5 ton residential air conditioning compressor
>needs to have a 50 amp circuit breaker at the meter box and then a second
>set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>
>Those 60 amp fuses seem to be a duplication IMHO and are a pain to change
>periodically.
>
>Regards,
>Mike
Read the nameplate label on the air conditioining condensing unit
really carefully - see what it says. Every word on there has meaning,
and you have to do a bit of parsing. If it has to have fuses, the
call out will not say anything about circuit breakers.
It will call for a Minimum Circuit Ampacity, and that's the minimum
feeder wire and circuit breaker at the main panel.
A bit bigger on the wire ampacity is always better, look at the
Locked Rotor Amps to see what the start current is - usually 10X the
Full Load Amps. That's why the lights dim, it's drawing 10X current
for that first half second as the motor spins up. Larger wire means
lower voltage drop and a faster start, less strain on the motor
windings, the compressor lives longer.
But when they call for a 'Maximum Fuse or Circuit Breaker Amps' or
'Maximum Fuse Amps' on the nameplate, you stick to that to protect
the motor from a burn-out. And the Locked Rotor Amps is why you need
to use time-delay fuses and/or a circuit breaker witrh a HVAC-R time
delay built in.
If the nameplate calls for a "Minimum Fuse Size" it has to have a
set of fuses somewhere in the feed line for protection. If the label
calls for "Minimum Fuse or Circuit Breaker Size" you do not need a
fused disconnect, just a safety switch within sight of the unit for
servicing.
There is a good reason for the duplication - While a breaker might
fail to open fast enough to protect the compressor motor if it doesn't
start properly (bad start capacitor, high head pressure, etc.), the
odds are much better that a set of fuses is going to open when needed.
On the flip side, the fuses are probably going to blow from old age
after 10 years or so, due to all those start surges slowly weakening
the elements. Them's the breaks.
The unit will probably need servicing after 10 years anyways, if you
know how and are willing to make some stiff investments in education
(including a refrigerant technician license) and specialized equipment
you can do this yourself.
If you don't want to drop a few grand on gear and spend some time to
learn how to do it yourself, you are far better off calling someone to
service it anyways.
--<< Bruce >>--
Proctologically Violated��
"Andrew VK3BFA" <VK3...@wia.org.au> wrote in message
news:78dfd793-ccaf-4b1d...@m7g2000prd.googlegroups.com...
=======================================
Well, this is sort of the thrust of this thread -- given the up-stream 50 A
breakers, why would copper rod be so unsafe? Or a wire jump?
The only thing I can think of is that oddball heating/connection issue --
which a screw-type wire jump would sidestep, anyway.
--
Mr. PV'd
Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
glad to see me??
Experiment on Homo Sapiens -- CEOs, Lawyers, and Politicians, in
particular.
Spare the animals.
Click here every day to feed an animal that needs you today.
www.theanimalrescuesite.com/
Otherwise, if nothing works, a prayer to whatever god you worship is
Lloyd E. Sponenburgh
> COMPRESSOR, R.L.A. 30. 8/30. 8 L.R.A. 178 <--not sure what this
means?
>
running load amps (at both the stated voltages) 30.8A
locked rotor amps 178A
It sucks roughly 6X running current when starting; that's the reason
for time-delay fuses or HACR style breakers.
Technically, the fuses are redundant. But fuses tend to more reliably
open under load than breakers do. If you're more interested in
protecting your AC than the inconvenience of servicing the fuses every
8-10years, then leave them in.
The reason one should not bypass fuses (even if they are not required)
is because by doing so, you have modified the function and purpose of
an approved electrical device. Doing so clears all bets off the table
in case of a fire.
LLoyd
Bruce L. Bergman
>The entire plate on the compressor:
>
>RHEEM MFG CO
>MODEL RAFD-060 JBS MFD 1-90
>SERIAL NO xxxxxxx OUTDOOR USE
>Volt 208/230 1ph, 60 hertz
>COMPRESSOR, R.L.A. 30. 8/30. 8 L.R.A. 178 <--not sure what this means?
>OUTDOOR FAN MOTOR FLA 2.0
>
>MIN SUPPLY CIRCUIT CAPACITY 40 AMP
>MAX FUSE OR HACR TYPE CKT BKR SIZE 60/60 AMP
>MIN FUSE OR HACR TYPE CKT BKR SIZE 50/50 AMP
>
>FACTORY TEST PRESSURE HIGH 300 PSIG
>FACTORY TEST PRESSURE LOW 150 PSIG
>OUTDOOR CIRCUIT FACTORY CHARGE 118 OZ R22
>TOTAL SYSTEM CHARGE <BLANK>
RLA - Running Load Amps - How much it draws at 208V /and 230V
LRA - Locked Rotor Amps - How much it draws on initital startup, or if
it can't start because there is still pressure in the system (short
cycling) or the compressor goes bad mechanically and jams.
You need to know these amp ratings to design the power feed circuit
and (if you are making your own electricity) to size the transformer
or generator plant feeding the unit.
Note that generators meant for Recreational Vehicle use often say
things like "Will start a 7,200 or 13,000 BTU Air Conditioner" in the
paperwork.
>I currently have 6 ga wire 50ft, 50 amp breaker at a 200 amp service panel
>and the 60 AMP SLO-LAG fuses at the shutoff box at the compressor.
>Lights do not dim when it starts.
>
>Are the 60 amp fuses needed or not?
>THIS IS NOT 100% CLEAR TO ME in spite of your excellent discussion.
It says "Fuse or HACR Rated circuit breaker" so the fuses aren't
absolutely necessary. Either will do. Get out a magnifying glass to
read the breaker label for the HACR rating, which won't be on
old-stock breakers.
But I would still leave the fuses in, because circuit breakers DO
fail to trip occasionally - or they do trip, but after far too long of
a time delay that allows compressor damage.
It's cheap insurance, so big deal if you have to replace the fuses
every 10 years or so.
>Regarding service:
>The last fuse lasted 9 years - before that I had nothing but problems -
>every week etc. Cleaned all surfaces an no real problem since <knock on
>wood!>
>
>No technician has checked the unit in more than 10 years and I see NO
>problem and I am EXTREMELY cautious about tampering with something that
>works. <GRIN>
>May this be doing damage to the unit - to not have (annual?) service?
So don't let it crap out!
When it's running, check that the big suction line headed out to the
condensing unit is still frosty cold - that's the quick and dirty test
that there's enough refrigerant in the system. The "leftover" cold in
the system is how the compressor motor gets cooled - the incoming cold
gas goes through the windings. If the refrigerant charge is too low,
you start slowly cooking the compressor motor to an earlier failure.
If it's low on refrigerant you WILL need to call someone to fill it
up, because you need a Refrigerant Technician License to buy the
refrigerant (Multiple Guess Test, simple once you grasp the
principles) and $1500 to $2500 worth of gear on hand to do it legally.
(Must have a refrigerant recovery machine and an empty recovery tank
on hand if a big leak starts, so it doesn't leak into the environment.
Silly, but I didn't write the laws I just try to follow them. And
when the EPA can fine you from $10,000 up to a Half-Million Bucks for
each violation, you have an incentive to follow the rules...)
Everything else, you can do.
Get some Non Acid condenser coil cleaner and a pressure washer, and
clean out the bugs and dirt from the condenser core outside. Let the
soap soak then pressure wash out the crud.
Get a can of self-rinsing evaporator core cleaner and get the gunk
off the inside coils. You can't use a pressure washer, so it rinses
off with the normal condensation.
Get a case of good High Efficiency air filters, and change them
every couple of months, or as they get filthy.
And make sure the condensate drains are clear, and the secondary drip
pan is under the unit if it's a horizontal in the attic, and a general
once-over.
Oil the fan motor bearings with non detergent 10W Turbine Oil, and
change the belt if the blower is belt drive. Same thing with the
condensing unit fan if it's oilable - look for the little black plugs
and OIL markings on the oil holes, and plug them again when finished
to keep the rain out.
Spin the fan and feel the bearings, if they are getting lumpy buy a
new motor. Not too hard to change, not worth the trouble to fix.
>My current plan is to buy 4 windows units when/if this unit craps out and
>requires $500+ repairs.
No you don't - window units are far less efficient, and give more
trouble. And depending on where you are, natural gas heat is a LOT
less expensive than electric or heat pump. Propane and Oil heat are
more, but still cheaper than electric. That old furnace and central
air is still worth keeping.
--<< Bruce >>--
Rich Grise
> Does anybody know why a 5 ton residential air conditioning compressor
> needs to have a 50 amp circuit breaker at the meter box and then a second
> set of two 'slo-lag' 60 amp fuses in a box next to the compressor?
>
> Those 60 amp fuses seem to be a duplication IMHO and are a pain to change
> periodically.
>
Why would you change fuses "periodically"? Until they blow, they're in
place indefinitely.
They're slo-blo, to let the compressor start, and if the compressor gets
stuck, they blow before the short burns the house down.
Cheers!
Rich
jk
>This time I have avoided operating the ON OFF handle since if it is
>corroded to a good connection - don't mess with it. Is this incorrect
>thinking?
Very.
NOTHING ever corrodes TO a good connection
jk
Bruce L. Bergman
>On Tue, 14 Jul 2009 11:50:37 -0700, Bruce L. Bergman
><bruceNOSP...@gmail.com> wrote:
>
>> When it's running, check that the big suction line headed out to the
>>condensing unit is still frosty cold - that's the quick and dirty test
>>that there's enough refrigerant in the system.
>
>
>> --<< Bruce >>--
>
>"Frosty cold" I read that as dry and with frost where a finger would stick
>like glue.
>I have what I would call 'very cold' but wet or damp with condensate.
>
>Does this unit past the test or is there some refinement?
>
>Mike
Very cold will do. When it hits "lukewarm" then you worry.