208V vs. 240V
Rob
Everything turned out great. Thanks to all for the help.
Now a slightly different question: My friend's apartment is located above a
restaurant. Recently here, they have switched the entire area to 3 phase
(208V). Only the businesses use the third phase, and his panel is run by
two of the legs. Can he use a shared neutral setup? Are the 2 hot wires
still out 180 degrees, or is it 120? Would a shared neutral cause problems
(ie, addition of outgoing current) in the neutral wire? I'm not 100 percent
familiar with the concept of 3 phase systems. Thanks for any ideas.
unknown
In a single phase system, the two hot legs are 180 degrees out of phase, and if
you drew equal current from both legs to neutral, there would be zero net
current in the neutral. Using two hot legs of a 3 phase system, with equal
loads between each hot leg and neutral, will NOT result in zero neutral current.
That's nothing to be concerned about, since the magnitude of neutral current
is still less than it would be for a single load connected between one hot leg
and
the neutral.
You have nothing at all to worry about from a safety standpoint.
What you should be aware of is that if there are any line-to-line connected
loads in the apartment (such as electric stove, electric oven, or electric
hot water heater), they will now be getting 208 volts instead of 240V,
which is only 87% of their rated voltage, so their heat-producing capacity
will be reduced to about 76% of what it was when they were on 240 volts.
No danger at all, but any heating element which was rated, say, 1500 watts
at 240 volts will now only produce about 1135 watts at 208 volts.
Water reheating (recovery) for an electric hot water heater will be slower,
as will some cooking.
Budys back
Rob...
Oh really? So, all these busisnesses suddenly had to rip out their single-phase
services and switch to 3-phase, because the "utility" decided to change their
distribution network?
Do your own homework kid.
Read the book.
Do your homework.
Read the book.
\\\///
From: (ô ô)
+oOO-----(_)-------------------------+
| Budys back |
+-----------------------------------------+
Daniel Hicks
[snip]
> What you should be aware of is that if there are any line-to-line connected
> loads in the apartment (such as electric stove, electric oven, or electric
> hot water heater), they will now be getting 208 volts instead of 240V,
> which is only 87% of their rated voltage, so their heat-producing capacity
> will be reduced to about 76% of what it was when they were on 240 volts.
>
> No danger at all, but any heating element which was rated, say, 1500 watts
> at 240 volts will now only produce about 1135 watts at 208 volts.
>
> Water reheating (recovery) for an electric hot water heater will be slower,
> as will some cooking.
Any 240V motorized equipment may be at risk. This would include
especially air conditioners. If they are not rated for 208V then they
will very likely burn out. IMO, someone (the people who wanted this
change) should pay to replace their AC units if there turns out to be a
problem.
Rob
this past winter wasn't as high (electric baseboard).
Rob
Budys back wrote in message
<20000416125635...@nso-cp.aol.com>...
>Rob...
>Oh really? So, all these busisnesses suddenly had to rip out their
single-phase
>services and switch to 3-phase, because the "utility" decided to change
their
>distribution network?
>
>Do your own homework kid.
>Read the book.
>Do your homework.
>Read the book.
>
>
>
>
> \\\///
> From: (ô ô)
> +oOO-----(_)-------------------------+
> | Budys back |
> +-----------------------------------------+
I don't quite understand your reaction. In actual fact, the utility paid
for all of the upgrades as I understand it. They were providing 600V and
120V before, now they only provide 208V. If you think I'm lying or
something, go ahead and call Toronto Hydro. They claimed that this new
service would be more reliable. It had better be, because even the
streetlamps are connected to it.
John Coggins
three-phase 208V supply. That's how it's done on a 208V system,
whether you have access to one hot leg or three.
Since there's only one neutral in a 208V wye-connected system (or a
240V, for that matter), I assume your reference to 'shared' is really
a question about the way the single phase circuits are actually wired:
2 hots and on neutral in the same cable, perhaps. That would depend on
local electrical code.
Hamm4fun
3 phase and they supply 1 or 3 phases of it to their customers not 2 or 3. 240
is single not 2 phase meaning it is derived from one phase of the power
companies 3 phase distribution system. What probably happened is that the power
company origional had only 1 phase coming into an area and because of increased
demand they brought in the other 2 phases. They could have had 2 phases coming
in and brought in the third. A typical residence or business still gets only
one of the three phases unless they specifically need three phase power for
something. Yes this mean more reliable power for the customer but you are still
240 not 208
Daniel Hicks
The problem is that the power TO THE BUILDING (apartment above a
restaurant) was changed from 240 to 3-phase.
Hamm4fun
Then get used to cold showers.
I used to work in a clothing plant that had three phase and nothing else
whenever we tried to use some 240 equipment on 208 it just worked half assed.
Daniel Hicks
The water heater elements can be changed to 208V units, if the apartment
has an electric water heater.
Budys back
(Hamm4fun) writes:
>This sounds really wierd to me. All the power generated by the power company
>is
>3 phase and they supply 1 or 3 phases of it to their customers not 2 or 3.
>240
>is single not 2 phase meaning it is derived from one phase of the power
>companies 3 phase distribution system.
In primary distribution thats true, but 120/240 is derived from 1 single phase
of the primary distribution system. When a utility provides "single phase" you
get 2 120v hot legs with 240 between them. When 3-phase is available, it's 208
between the phases and must be deried from all 3 primary phases.
In an area with mixed commercial/residential services, it's not uncommon to
feed the residential customers with 2 of the 3 phases, but it is only 208 and
different from the more common 120/240v residential service.
I'd like to know how the utility balances this type of load though...
TimothyBil
>feed the residential customers with 2 of the 3 phases, but it is only 208 and
>different from the more common 120/240v residential service.
>
I don't think so. In a mixed commercial/residential area, it is very common to
see 6 wires running to some of the buildings (mixed 240 1ph & 208 3ph), four
wires to some (208 3ph) and three to others (240 1ph). Usually the power
company will step down from the last intermediate voltage to 208 3ph for the
distribution wires, and periodically add a 208 to 240 transformer to one phase
to provide 240 as needed. As long as the 208 - 240 transformers are evenly
spread on all three phases, the load stays pretty well balanced. I would find
it very hard to believe that any power company would introduce a permanent 15%
voltage drop in any of it's customers by switching them from 240 to 208.
Scott E. Thompson
Wye connected transformer when either the original Delta connected secondary type
transformer burned out, or a car hit the pole. Seen it done in a lot of areas with older
services feeding both Commercial and Residential customers. It is safer to have the Delta
connection taken out and replaced with the Wye connection so the 3 phase customers do not
have the Wild Phase to deal with and the consequences of connecting a 120 volt load to the
208 volts to ground high leg.
Other reasons that the system may have been changed to a Wye is that the 4 KV primaries
are being "Phased Out" in favor of using the 12 KV primaries. This is something I have run
across when working in older sections of cities. The Utility company's design engineers
will try to get a new or upgraded service to be on the 12 KV primaries when the original
was on he 4 KV primaries.
The line to line loads [208 volt] that are resistive [such as electric ovens, stoves and
water heaters] will have a lower heating ability at the lower voltage than they did
before.
Motors will tend to draw more current to deliver the same HP, but unless they should not
get overheated unless they are run near their maximum HP for some time.
All line to ground [120 volt] loads will operate as they did before.
Reply directly to me if any questions.
Scott.
Daniel Hicks wrote:
> unknown wrote:
> [snip]
> > What you should be aware of is that if there are any line-to-line connected
> > loads in the apartment (such as electric stove, electric oven, or electric
> > hot water heater), they will now be getting 208 volts instead of 240V,
> > which is only 87% of their rated voltage, so their heat-producing capacity
> > will be reduced to about 76% of what it was when they were on 240 volts.
> >
> > No danger at all, but any heating element which was rated, say, 1500 watts
> > at 240 volts will now only produce about 1135 watts at 208 volts.
> >
> > Water reheating (recovery) for an electric hot water heater will be slower,
> > as will some cooking.
>
> Any 240V motorized equipment may be at risk. This would include
> especially air conditioners. If they are not rated for 208V then they
> will very likely burn out. IMO, someone (the people who wanted this
> change) should pay to replace their AC units if there turns out to be a
> problem.
>
> > Rob wrote:
> >
> > > A while back I asked about wiring up a double-pole breaker situation.
> > > Everything turned out great. Thanks to all for the help.
> > > Now a slightly different question: My friend's apartment is located above a
> > > restaurant. Recently here, they have switched the entire area to 3 phase
> > > (208V). Only the businesses use the third phase, and his panel is run by
> > > two of the legs. Can he use a shared neutral setup? Are the 2 hot wires
> > > still out 180 degrees, or is it 120? Would a shared neutral cause problems
> > > (ie, addition of outgoing current) in the neutral wire? I'm not 100 percent
> > > familiar with the concept of 3 phase systems. Thanks for any ideas.
--
This Was Sent By:
Scott Thompson / Thompson Electric
ad...@SoCA.com
PC # 2
Terry Kennedy
> I would find
> it very hard to believe that any power company would introduce a permanent 15%
> voltage drop in any of it's customers by switching them from 240 to 208.
My house (on a purely residential block) has been supplied by the utility
with 208V for at least 30 years. As have the rest of the houses on this
block and many nearby blocks.
Of course, this is PSE&G, who make NYC's ConEd look like a paragon of
modernity - PSE&G still hasn't figured out how to read the electric meters
from outside the house using extenders, though (oddly) they do offer this
for their gas meters.
Terry Kennedy http://www.tmk.com
te...@tmk.com Jersey City, NJ USA
Greenlight
3 phase wye and delta, thanks. In the beginning of this thread it was asked
if the original single phase 120v/240v circuits that share a common neutral
would be affected. The answers given by others was correct, no difference
there. That is the advantage of 3 phase 208 volt wye. However in this case
what occurred is that the existing commercial building became "upgraded"
from SINGLE phase 120/240v to 3 phase 208 (wye). This type of "upgrade"
gives the tenants more 120 volt options as the voltage to ground between all
three phases are 120 volts (as you know). This is preferred in many office
buildings and mixed residential use where "most" loads are 120 volts.
However Dan is right, that many 240 volt applications may suffer. That is
why 3 phase Delta (240 volts per each phase, but 120 volts only between TWO
phases -- Red Leg or High leg) are preferred only in Industrial applications
where there usually are many more 240 volt motor loads). You guys already
know that, but I wanted to summarize this for Rob to explain why 208 was
chosen in his situation versus 249 volt Delta. The next common question
would be why didn't they change it to 240 volts between all three phases
WITH 120 volts between ALL three phases to ground. That would be preferred
but is beyond their technical ability for reasons we will not elaborate upon
(transformer and electrical generation and distribution theory).
As "unknown" said, resistive loads like electric heaters will probably not
be greatly affected taking only a 20% drop in output, but as Dan pointed out
some types of 240 volt motors may actually operate hotter or even stall, but
this potential problem can be foreseen and corrective measures taken. In
general much more usable 120 volt power is now available at the building by
simply switching from single phase to three phase wye.
hitman
>This sounds really wierd to me. All the power generated by the power company is
>3 phase and they supply 1 or 3 phases of it to their customers not 2 or 3. 240
>is single not 2 phase meaning it is derived from one phase of the power
>companies 3 phase distribution system. What probably happened is that the power
>company origional had only 1 phase coming into an area and because of increased
>demand they brought in the other 2 phases. They could have had 2 phases coming
>in and brought in the third. A typical residence or business still gets only
>one of the three phases unless they specifically need three phase power for
>something. Yes this mean more reliable power for the customer but you are still
>240 not 208
Wow, a knowledgeable response.
__________________________________________
The more you own the more you have to fix!
Lin and Ron
Sebastian Fl, formerly NJ
(Maplewood, Neptune, Bricktown[Laurelton], Toms River)
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Budys back
(hitman) writes:
>A typical residence or business still gets only
>>one of the three phases unless they specifically need three phase power for
>>something. Yes this mean more reliable power for the customer but you are
>still
>>240 not 208
>Wow, a knowledgeable response.
And larggely incorrect, as the "typical" business or residence gets 2 "Phases"
from a "single phase" primary.
Don Klipstein
: >In an area with mixed commercial/residential services, it's not uncommon to
: >feed the residential customers with 2 of the 3 phases, but it is only 208 and
: >different from the more common 120/240v residential service.
: >
:
: I don't think so. In a mixed commercial/residential area, it is very common to
: see 6 wires running to some of the buildings (mixed 240 1ph & 208 3ph), four
: wires to some (208 3ph) and three to others (240 1ph). Usually the power
: company will step down from the last intermediate voltage to 208 3ph for the
: distribution wires, and periodically add a 208 to 240 transformer to one phase
: to provide 240 as needed. As long as the 208 - 240 transformers are evenly
: it very hard to believe that any power company would introduce a permanent 15%
: voltage drop in any of it's customers by switching them from 240 to 208.
I can mention one thing I have seen in an industrial working class
neighborhood of Philadelphia:
Three phase, with each phase being 120/240 connected "Wye". This would
give six 120 volt "phases" if the center taps of all three phases were
connected to neutral.
But one phase is different, with one end of that phase being neutral and
the midpoint being one of the 120 volt points and the end point being a
240 volt "High Leg". If all phases are available, there are five 120 volt
points, 60 degrees apart, with the sixth one missing since it is opposite
the high leg. The midpoint of the high leg and two of the other 120 volt
points are 208 volts line-to-line 3-phase.
- Don Klipstein (d...@misty.com)
scot...@my-deja.com
Glad to be back.
I had to subscribe to Dejanews because Pacbell's news server is
having some personel problems :-)
I haven't replied to any posted replies due to this problem.
Let's see how everything turns out this time around.
P.S.: hows our favorite friend doing ??
Reply to me directly for best results !!
Scott
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