I live in a warehouse that has two main circuit panels: one is
split-phase (1-phase) which powers most of the 120v electricity in the
warehouse, and a second panel that is 3-phase (once used for shop
equipment likt a compressor and lathe)-they are located in opposite
sides of the building. Instead of running new electrical conduit
through the warehouse, I want to use this 3-phase circuit panel for
120v outlets, lights, etc., and I have researched that I am dealing
with a 3-phase situation refered to as "Delta Wild Leg 240v." I have 3
hot wires (A, B(wild) & C), I can run all my 120 stuff off A to neutral
or C to neutral.
I have these questions:
1) Should I just pull the 3 phase circuit panel and disconnect the B
cable, install a single phase panel in it's place and I am good to go?!
2) Just continue to use the 3-phase circuit panel and only use lines A
and C to Neutral for 120/220v applications and leave open/free/unused
the "Wild Leg" B line. It leaves me with less connecitons, but I can
probably make due.
It seems a bad idea to remove this 3-phase power (since I hear it is
expensive to install), but then it seems strange to leave unused
circuit breaker sections of a circuit panel...
Does anyone have any recommendations? Thanks in advance.
You should confirm that there is a neutral in the three phase panel. It is
not uncommon to have a three phase delta panel without a neutral conductor.
If so then go ahead and use phases A and C for your 120 volt circuits. If
it isn't already identified, it is a good idea to mark the outside of the
panel indicating the high B phase.
In my area in NC we have a "high leg" on the 3 phase. One of the wires have
higher voltage than 120. I would check to see if you have this. I have had
electricians here that did not realize it until I told them. I think it goes
up to 140V on one wire. One electrician told me he burned a bunch of record
players in a bar by knowing this fact.
As others said, leave the existing panel in place. After you verify
that there is a (GROUNDED) Neutral, plug in breaker(s) as needed.
But before you do any of this, you had better contact the utility
and find out what the current (no pun) billing arrangements are.
If your (puny?) load is all that will be on the service, they may
object to continue provisioning the service.
If some one else is *still* using and paying for this service,
you have other problems to iron out.
First, thanks to everyone that responded.
I have already tested the voltage for each hot line, so I am sure as to
which line (the "B" line) is the Wild Leg. Since this is the first
time I have come into contact with a Delta system (although I have done
enough electrical wiring in the home to feel comfortable around
electrical installations), I just needed to make sure I wasn't
operating outside of safety limits.
It is interesting to me how three-phase comes into the warehouse, and
at the main breaker (just after the meter), two hot lines are split
off, so that 2 hots (A, B) plus a Neutral go to one 120/220v panel and
three hots (A, B, C) and a Neutral go to another 120/208/120v panel. Of
course, there is also a main grounding cable running off to a water
pipe as well.
I don't think there will be any problem with my utility, as the
warehouse is rated commercial/residential, and if there ever is a
problem...well, I'll just go and adjust the Delta system.
But, I do have a follow up question: In both my circuit panels, the
ground connector bar is not connected to the Neutral Connector bar. I
was reading up on my electricity configurations and I saw mentioned how
the Main Circuit Panel should have it's Grounding Connecter Bar
connected to the Neutral Connector Bar (and to NOT do this in any
subpanels). Is this correct? While the wiring in this warehouse is
grounded to metal electrical boxes in some places and in other places
there are grounding copper lines to electrical conduit that is attached
to the Main Circuit Panel. The 3-phase circuit panel does NOT have the
Grounding Bar connected to the Neutral Bar.
Since you have a main breaker the neutral and the ground are probably bonded
there or possibly in the meter. The two electrical panels therefore should
NOT have the neutral and ground bonded together. The ground and neutral
must remain separated.
If you use 3 phase power for 120V applications then you should try to
balance the load on each of the phases. If you don't then the neutral may
float above ground a few volts. Another point is you don't have 240V
available. There is 208V between any two of the hot legs because they are
only 120 degrees out of phase with each other. Many motors are rated to run
on either voltage be sure to check if 208 is ok if you are going to use a
The real advantage of running 3 phase motors is that they are drawing
constant power and so run smoother than 2 phase motors where the power goes
to zero 120 times a second. Same for generators. That is why you always
see high voltage lines in groups of three.
No. He doesn't have a 120/208V WYE service.
This is a DELTA service with 240V between each leg.
The C.T. of one transformer is grounded, giving 120V to
He can not "balance" loads because he can only connect
to that one transformer winding with the C.T.
This is a totally different situation than the common 120/208 WYE.
> If you use 3 phase power for 120V applications then you should try to
> balance the load on each of the phases. If you don't then the neutral
> may float above ground a few volts. Another point is you don't have
> 240V available. There is 208V between any two of the hot legs because
> they are only 120 degrees out of phase with each other. Many motors
> are rated to run on either voltage be sure to check if 208 is OK if
> you are going to use a 240V appliance.
> The real advantage of running 3 phase motors is that they are drawing
> constant power and so run smoother than 2 phase motors where the power
> goes to zero 120 times a second. Same for generators. That is why
> you always see high voltage lines in groups of three.
The custom on Usenet is to post your reply below any quoted part of the
message you are replying to. This makes it easier for everyone else to
follow the conversation.
"According to the IEEE Dictionary, a neutral conductor is the conductor
with an equal potential difference between it and the other output
conductors of a 3- or 4-wire system. Therefore, a neutral conductor is
the white/gray wire of a 3-wire 120/240V single-phase or 4-wire 120/208V
or 277/480V three-phase wye-connected system. Figure 250-7
Since a neutral conductor can only originate from a 3-wire single-phase
or 4-wire wye system, the white wire of a 2-wire circuit or the white
wire from a 4-wire 120/240V three-phase delta-connected system isn't a
neutral conductor – it’s a grounded conductor." Mike Holt website.
It is apparent that you do not know the difference between delta and wye
connected three phase power. When the utility provides three phase
delta power the transformers; or, more rarely, the three windings of a
single transformer; are connected with each end of the secondary winding
connected to the end of another transformers secondary winding. None of
the transformers / windings are connected to the grounded conductor at
the end of it's winding. Instead one of the transformers / windings is
center tapped and the grounded conductor is connected at that center
tap. This A to C phase transformer is often larger than the other two
because it must carry all of the 120 volt loads in the premise served.
The output voltage of each transformer across it's entire winding is in
fact 240 volts. The voltage between the grounded conductor that is
connected to the A to C transformer center tap and the conductor that is
connected to the B phase of this service will be higher than the voltage
from A to Ground or C to ground. that is why that phase is called the
wild or stinger leg. The US NEC requires that the phase with the higher
voltage to ground be marked with orange markings at all accessible
points in order to warn of this higher voltage to ground. NO load is
connected between the grounded conductor and the B phase because the
voltage on the B phase is approximately 208 volts to ground.
Well we aren\'t no thin blue heroes and yet we aren\'t no blackguards to.
Dont't forget about Open Delta, where instead of 3 transformers connected
in a delta configuration, with the center point of one winding grounded,
the utility cuts corners, and only provides 2 transformers, with one leg
(A-C) being center tapped, and the other (A-B) being the wild leg. The third
(B-C) connection between the wild leg and the other end of the center tapped
winding is omitted.
This configuration is frequently provided where there is a small requirement
for 3 phase power, but not enough to justify (in the eye of the utility) a
full delta service. It is not as stable as a full delta, and some equipment
dosen't like it (broadcast transmitters, etc..)
Another service is Corner Grounded Delta, where instead of having one
transformer center tapped, one corner of the delta is grounded.
This configuration does not allow for any split voltages (120/240, 240/480),
everything is phase-phase.
Oh, and thinking back to the original question, which is already on the
cutting room floor.. He could add a single-phase subpanel, tapped from
the 3 phase panel, and avoid the worry about accidently connecting to the
-- Welcome My Son, Welcome To The Machine --
Bob Vaughan | techie @ tantivy.net |
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