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#4696 - 10/12/01 11:13 AM Electrical Design Issues: White Paper  
SC Surfer Dude  Offline
Junior Member
Joined: Oct 2001
Posts: 3
Charleston, SC USA
Good day to all,

I have been asked to write a White Paper to address power concerns below, and I was wondering if there are any good thoughts or documents out there?

This effort was a result of numerous concerns that questioned whether design plans were sufficient to prevent damaging building and equipment, injuring personnel, and allowing communications equipment to be installed and tested in an efficient manner.

208/120 VAC, 60 Hz, 3Ø

(2 Siemens, S1 Panelboards, 2 panels each platform, 42 circuits, 150A MCB’s each, Panelboard restricted to 250A Max. by a 225A Main Service Panel Breaker)

Amps available 300 AMPS

Potential Shortfall: -400 AMPS for simultaneous equipment usage?

Thanks a bunch,
"Proud To Be an American"
SC Surfer Dude



[This message has been edited by SC Surfer Dude (edited 10-15-2001).]


Work Gear for Electricians and the Trades

#4697 - 10/13/01 10:13 AM Re: Electrical Design Issues: White Paper  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,259
Fullerton, CA USA
SCSD,
Your question is kind of difficult for me, and possibly others, to understand.
Although most case specific Q's can be answered by the guys here on the BB, could you rephrase this in a way that we are more accustomed to?
(Also, you might want to verify the voltage. 115V, 60Hz, 3Ø is not a common standard)


#4698 - 10/15/01 11:37 AM Re: Electrical Design Issues: White Paper  
WARREN1  Offline
Member
Joined: May 2001
Posts: 176
Greenville, SC, USA
SCSD
Like Electure says, I think we are not sure what you are asking.
I am not familiar with Siemens panelboards, but could look up specifics from a catalog. Need to know your question.
Panelboard mounted on a platform need to have seveal questions addressed. First, is how much working clearance do you have? Accessibility?
With a 225A Main Breaker, the max. limitation will be 225A, except for inrush current of a short duration.
Where is the 300Amps available coming from? An upstream panelboard or switchboard breaker?
Are you expecting 400Amps of continuous power consumption?


#4699 - 10/15/01 02:07 PM Re: Electrical Design Issues: White Paper  
SC Surfer Dude  Offline
Junior Member
Joined: Oct 2001
Posts: 3
Charleston, SC USA
Electure and Warren1,

What we have is a 480 VAC, 3Ø, 60 Hz, Main Service Panel with 225 Main Circuit Breakers feeding two Siemens S2 Panelboards. We have a 45 KVA 480 VAC - 208/120, 3Ø, 60 Hz stepdown transformer which feeds our S1 Siemen Panelboards (2 each) via a 150 A Main Circuit Breaker. One of the 208/120, 3Ø Panelboards is loaded (Max Design) with a balanced load of 264.7 A and the 2nd is balanced with 174.0 A per phase. My supervisors are sweating bullets and don't understand non-coincidental loading and demand factor. If you look at the maximum loading and nothing else, which is what my supervisors are doing, it might look bad. The NEC 1999 doesn't make these guys feel any more comfortable. They are more interested in cutting the Main Panel breakers back to 50 Amps.

Thanks,

SC Surfer Dude
"Charley South"


#4700 - 10/17/01 06:41 PM Re: Electrical Design Issues: White Paper  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,259
Fullerton, CA USA
I still don't quite get what you're asking, but
Is there a reason that these loads couldn't all coincide, or just that they haven't yet.
You might try putting a recording ammeter for a while to see what it really draws.


#4701 - 10/18/01 03:45 AM Re: Electrical Design Issues: White Paper  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Surfer Dude,

I have a few questions and comments as to your installation.

<OL TYPE=1>

[*] The service is 480Y/277, with a 225 amp main OCPD - is this correct? Do you need upto 100 KVA for this installation?
If you plan to run the service to maximum, better verify that the utility transformer and feeders can handle that load.
With a 225 amp main at the service, you would need at least 100 KVA available from the utility transformer if you plan to run upto 225 amps [less than 3 hours].
Nevertheless, your total ratings listed in the first message reflect the Panel's listed rating of the bus kits (250 amps).
The 150 amp Subfeeder OCPD will equal out to be either 150 max on 1 panel, 75 on the other - or 112 amps on both panels. Total amperes available: 225 amps maximum [pending utility transformer size, fusing and feeder size].

[*] The 480 x 208Y/120 3ph 4 wire transformer is 45 KVA correct? This would be max fused / OCPD on the primary side of 60 amps (45 KVA xfmr @ 480 VAC = 54 amps.. I think! pulling numbers from memory!).
The Secondary would be protected by maximum 150 amp OCPD (should be something like 125 amps @ 208 VAC).
Per L-G circuit (120 VAC 1ph 2 wire), there's 15 KVA available, so that's another thing to consider.
</OL>

Consider adding to your White Paper / System Performance Report these items:

*Completed Panel Schedule[s] [denote LCL's, coincidental loads, etc.]. A simple "Load Calc" will also work here, and can be used in conjunction with the Panel Schedule.

* 1 Line riser / feeder diagram. Denote service feeder size and utility transformer design size and current load.
Here in So California, SCE figures a transformer to be loaded beyond capacity when there's a total LCL load above 130% the rated KVA of the transformer.
This was prior to Deregulation [Linked Image]

* Breakdown of loads and their duty cycles.

Just how much of a peak load does this installation have? It's a Cell Site, isn't it?
Very curious to the equipment load values and duty [duration of peak power, duration of standby, normal load value, what loads are coincidental, etc.].

Scott SET

[This message has been edited by Scott35 (edited 10-18-2001).]


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#4702 - 10/19/01 10:28 AM Re: Electrical Design Issues: White Paper  
SC Surfer Dude  Offline
Junior Member
Joined: Oct 2001
Posts: 3
Charleston, SC USA
Alcon:

Radio Communications equipment to be installed and tested:

208/120 VAC, 60 Hz, 3Ø

(2 Siemens, S1 Panelboards, 2 panels each platform, 42 circuits, 150A MCB’s each, Panelboards restricted to 250A Max., each panelboard has an Over Current Protection Device (OCPD) @ 225A Main Circuit Breaker).


First, is how much working clearance do you have? Accessibility? Not an issue, 20 feet above, 5 feet all the way around.


What we have is a 480 VAC, 3Ø, 60 Hz, Main Service Panel with two (2) OCPD 225 Main Circuit Breakers (1 for each panelboard), feeding two Siemens S2 Panelboards. We have a 45 KVA 480 VAC - 208/120, 3Ø, 60 Hz stepdown transformer which feeds our S1 Siemen Panelboards (2 each) via a 150 A Main Circuit Breakers.

One of the 208/120, 3Ø Panelboards is loaded (Max Design) with a balanced load of 264.7 A and the 2nd is balanced with 174.0 A per phase.

Is there a reason that these loads couldn't all coincide, or just that they haven't yet? That is a problem if they decide to test all the communications transmitters, crypto, racks at the same time. They must understand that they can’t.

You might try putting a recording ammeter for a while to see what it really draws. That is a great idea, or at least use some clamp-on ammeters.

----------------------------------------------------------------------------------------
I have a few questions and comments as to your installation.

1. The service is 480Y/277, with a 225 amp main OCPD for each 208/120 VAC, 3Ø, S1 Panelboards (2).

2. Do you need upto 100 KVA for this installation? Yes, 100 KVA or more.

3. If you plan to run the service to maximum, better verify that the utility transformer and feeders can handle that load. Fed from a 1000 KVA, 4160/480Y VAC, 3Ø, ABB Padmount Transformer, using 10 feet of Essex 350 MCM Type THHN cable, to a Siemens, Main Switchboard, Cat. No. SB, 1200 A main Service Disconnect.

4. With a 225 amp main at the service, you would need at least 100 KVA available from the utility transformer if you plan to run upto 225 amps [less than 3 hours].
Nevertheless, your total ratings listed in the first message reflect the Panel's listed rating of the bus kits (250 amps). The 150 amp Subfeeder OCPD will equal out to be either 150 max on 1 panel, 75 on the other - or 112 amps on both panels.

Total amperes available: 225 amps maximum for each panelboard [pending utility transformer size, fusing and feeder size].

5. The 480 x 208Y/120 3ph 4 wire transformer is 45 KVA correct? Yes, this is correct. This would be max fused / OCPD on the primary side of 60 amps (45 KVA xfmr @ 480 VAC = 54 amps.. I think! pulling numbers from memory!).
The Secondary would be protected by maximum 150 amp OCPD (should be something like 125 amps @ 208 VAC). Correct
Per L-G circuit (120 VAC 1ph 2 wire), there's 15 KVA available, so that's another thing to consider.

Consider adding to your White Paper / System Performance Report these items:

&#61623; Completed Panel Schedule[s] [denote LCL's: = ?, coincidental loads, etc.]. A simple "Load Calc" will also work here, and can be used in conjunction with the Panel Schedule.
&#61623; 1 Line riser / feeder diagram. Denote service feeder size and utility transformer design size and current load.
&#61623; Here in So California, SCE figures a transformer to be loaded beyond capacity when there's a total LCL load above 130% the rated KVA of the transformer.
This was prior to Deregulation
&#61623; Breakdown of loads and their duty cycles.

Just how much of a peak load does this installation have? It's a Cell Site, isn't it? No-way Jose.

This is a Space and Naval Warefare (SPAWAR) test and integration facility for radio communications circuits (UHF, HF, SATCOM, EHF, etc.)

Very curious to the equipment load values and duty [duration of peak power, duration of standby, normal load value, what loads are coincidental, etc.].

We have approximately 30 Racks of communications gear (0.8 amps upto 35 amps), per ship (3 ships at a time, 2 panelboards per ship for all their 208/120 VAC, 3Ø, circuits).

A snapshot was taken earlier this year at a different building for the 208/120 panels, using AWG 2, THWN cable:

Phase A = 74.0 amps
Phase B = 67.6 amps
Phase C = 67.7 amps


Thanks a bunch,

SC Surfer Dude



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