ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
Trumpy 5
Recent Posts
What do you do?
by ghost307. 09/22/17 08:26 AM
Another generator question
by gfretwell. 09/21/17 02:41 PM
Supporting conduit bodies
by ghost307. 09/18/17 12:12 PM
Thermal Imaging Camera upgrade
by Potseal. 09/18/17 11:57 AM
Linear Power Supply Quits Under Load
by JoeTestingEngr. 09/15/17 11:37 PM
New in the Gallery:
Gallery Test
Popular Topics(Views)
240,860 Are you busy
176,619 Re: Forum
168,533 Need opinion
Who's Online Now
0 registered members (), 38 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
Page 1 of 2 1 2
#73229 - 12/20/06 09:43 AM 3 phase panel  
kyelectric  Offline
Member
Joined: Aug 2005
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!


Work Gear for Electricians and the Trades

#73230 - 12/20/06 09:48 AM Re: 3 phase panel  
Jps1006  Offline
Member
Joined: Jan 2004
Posts: 615
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.


#73231 - 12/20/06 03:07 PM Re: 3 phase panel  
ghost307  Offline
Member
Joined: May 2005
Posts: 911
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

#73232 - 12/20/06 07:50 PM Re: 3 phase panel  
kyelectric  Offline
Member
Joined: Aug 2005
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.


#73233 - 12/20/06 11:32 PM Re: 3 phase panel  
Rich Thomas  Offline
Member
Joined: Mar 2005
Posts: 48
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.


#73234 - 12/21/06 01:27 AM Re: 3 phase panel  
SolarPowered  Offline
Member
Joined: Jul 2004
Posts: 625
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.


#73235 - 12/21/06 01:43 AM Re: 3 phase panel  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
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. [Linked Image] (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. [Linked Image]


Stupid should be painful.

#73236 - 12/21/06 02:37 AM Re: 3 phase panel  
SolarPowered  Offline
Member
Joined: Jul 2004
Posts: 625
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.


#73237 - 12/21/06 03:27 AM Re: 3 phase panel  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,222
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

#73238 - 12/21/06 11:00 AM Re: 3 phase panel  
kyelectric  Offline
Member
Joined: Aug 2005
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.


Page 1 of 2 1 2

Member Spotlight
Bill Addiss
Bill Addiss
NY, USA
Posts: 3,878
Joined: October 2000
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.016s Queries: 15 (0.002s) Memory: 0.8181 MB (Peak: 0.9949 MB) Zlib enabled. Server Time: 2017-09-22 15:24:59 UTC