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#73229 - 12/20/06 05:43 AM 3 phase panel
kyelectric Offline
Member

Registered: 08/30/05
Posts: 64
I am doing some work for a company that has provided a 50 amp service with 3 phase 4 wire 120-208 Volts. With this new service panel, I am supposed to wire in 5 heaters @ 5kVA, lighting, GFCI protected receptacles, a water heater and exhaust fans. I don't believe there is enough power. The heaters all run off of single phase 208V. The lighting will run off of 120V. The water heater will run off of 208V. The exhaust fans are 120V. The company electrician said it should be enough power because it's 3 phase. My point is that none of the devices are using the 3 phase. There may be 33% more power available because of the extra leg but how do I add up the watts of this 3 phase panel to prove to them and to me that it's not enough power? Thanks!

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#73230 - 12/20/06 05:48 AM Re: 3 phase panel
Jps1006 Offline
Member

Registered: 01/22/04
Posts: 609
Loc: Northern IL
50 amps X 120 volt
+
50 amps X 120 volt
+
50 amps X 120 volt
-------------------

or

50 amps X 1.73 X 208

That is your available wattage.

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#73231 - 12/20/06 11:07 AM Re: 3 phase panel
ghost307 Offline
Member

Registered: 05/09/05
Posts: 884
Loc: Chicago Illinois USA
Gee, I wonder what the "company electrician" will say when it gets wired up and there isn't enough power to run the lights, fans and 25kW of electric heat from the available 18kVA service panel??

Tell the nice folks that the heaters are 5,000 Watts apiece; they have 18,000 Watts (I know, I'm ignoring power factor) to spend. They can run whatever they want, but it can't be greater than 18,000.

Remember the TV show "Green Acres"? Each appliance had a number on it and Lisa couldn't plug in anything more than "7". Same concept, different characters.
_________________________
Ghost307

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#73232 - 12/20/06 03:50 PM Re: 3 phase panel
kyelectric Offline
Member

Registered: 08/30/05
Posts: 64
Thanks for the info. I had calculated all of the watts at the voltage it was using. Then I added all the watts together and got a total. Then I divided the power by 208 V times the square of 3. After I did this I came out with 63 amps per leg which is already over the 50 amp breaker installed. The stuff I listed was just the big stuff. There was still more to add. I already called and informed someone higher up of the problem. He assured me that it would be taken care of.

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#73233 - 12/20/06 07:32 PM Re: 3 phase panel
Rich Thomas Offline
Member

Registered: 03/09/05
Posts: 48
Loc: Seattle, Washington, USA
I have two items, each of which may be non-sense considering your situation, but I need to mention them.

1. If the 5 heaters are controlled so that only 2 or 3 run at the same time, 50 Amps may be enough.

2. When you say 50 Amps service, do you mean there are 50 Amps available, or is this the trip rating of the secondary breaker? If it's the trip rating, the transformer may not be an 18KVA, but only a 10KVA with a full load capacity of only about 41 amps.

Anyway, those are my thoughts for what they're worth.

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#73234 - 12/20/06 09:27 PM Re: 3 phase panel
SolarPowered Offline
Member

Registered: 07/05/04
Posts: 615
Loc: Palo Alto, CA, USA
 Quote:
Remember the TV show "Green Acres"? Each appliance had a number on it and Lisa couldn't plug in anything more than "7". Same concept, different characters.

Really?! I sure do remember that show. When they first moved to the farm, and the electric company was installing the meter, she kept telling the POCO guy that they a bigger "electricical" (pronounced, "ee-lec-tri'-si-cle"). I guess she was right! I never noticed that part of it.

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#73235 - 12/20/06 09:43 PM Re: 3 phase panel
mxslick Offline
Member

Registered: 10/24/04
Posts: 785
Loc: Atomic City, ID USA
I thought on "Green Acres" that the "Rule of Seven" was only during the time they had one of Mr. Haney's generators. (Which BTW blew up in a show of sparks several times each show!!)

But I do remember that their POCO had "Peter The Meter Reader" and "Haller The Installer!!"

Classic (American) fluff T.V.
_________________________
Stupid should be painful.

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#73236 - 12/20/06 10:37 PM Re: 3 phase panel
SolarPowered Offline
Member

Registered: 07/05/04
Posts: 615
Loc: Palo Alto, CA, USA
 Quote:
I thought on "Green Acres" that the "Rule of Seven" was only during the time they had one of Mr. Haney's generators.

Yah, you're probably right. As I said, I'm not recalling that the "electricical" was actually too small after it was installed. So that would make sense, that it was Mr. Haney's generator.

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#73237 - 12/20/06 11:27 PM Re: 3 phase panel
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
To a degree KY,
You will have to balance that lot over 3 phases.
It's not about loads, but line currents, with respect to the Main Neutral.
If you have everything balanced, the Neutral will carry very little current.
50A per phase here in New Zealand is a pretty normal sort of a supply to farms and houses in a rural area, (although at 230/400V)
It's all about balancing everything over the 3 phases provided.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#73238 - 12/21/06 07:00 AM Re: 3 phase panel
kyelectric Offline
Member

Registered: 08/30/05
Posts: 64
The sub-panel that was installed by the company just for this addition is a main lug panel. There is a 50 amp 3 phase breaker in the panel just a few feet over that feeds the sub-panel. It's a 3 phase 4 wire 120-208 with #6's ran as the feeder wires to the sub-panel.

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