Power poles

[sjaniga]

We have been asked to supply power poles outside to a semi truck garage, we need 50 20-amp GFCI receptacles and each recept will handle 1200 watts of continuous load. This situation would be equivelant to a boat marina set up.

My questions are:
1. would it be better to bring out larger amp feeders for let say ten trucks to a j-box on each pole and tap for a 20-amp circuit?
2. what are the limitations of tapping for this situation?

Your input is appreciated,
Scott.

 

[hurk27]

Re: Power poles

each receptacle will handle 1200 watts of continuous load.

How continuous?
If all these receptacles will be in use at the same time your talking about 50@1200 watts = 60,000 watts or 500 amps @ 120 volts or 250 amps @ 240 volts.

To answer your question is I don't think so. Receptacles have to be protected by a breaker sized by table 210.21(B)(2). this means even a 20 amp receptacle can only hav a 20 amp breaker protecting it if you were to run a 100 amp protected circuit out to each set of 10 receptacles you would be in violation of 210.21


210.21 Outlet Devices.
(2) Total Cord-and-Plug-Connected Load. Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).


Table 210.21(B)(2) Maximum Cord-and-Plug-Connected Load to Receptacle

Circuit Rating (Amperes) Receptacle Rating (Amperes) Maximum Load (Amperes)
15 or 20 15 12
20 20 16
30 30 24

If these receptacles will not all be used at the same time then maybe put every other one one the same 20 amp breaker but this will cause problems if someone plugs in two trucks at the sometime.

we have done several wast-haulers depots and had to do this for the block heaters. But we used a 200 amp weatherproof panel mounted in the center of the receptacles and just ran separate circuits to each receptacle.

 

[sjaniga]

Re: Power poles

How continuous?

All 50 will be controlled by a timer/contactor to energize between 3am and 6:30am.

Thanks for the reply,
Scott

 

[hurk27]

Re: Power poles

But will all 50 have a load on them at the same time?
if so then two 200 amp panels would be the min. you could install unless you have 3-phase available then you could get away with a 200 amp panel but in any case you have to protect these receptacles with no more than 20 amp breakers. and if the connected load is 1200 watts then each would have to be on a separate circuit. this would still require at least two panel since you may only have 42 OCP's in one panel and going with two 125 amp panel would mean that they would be over the 80% rating of the panels, then I would use ether 150, 200 amp panel. this would allow for future expansion. bringing out 50 circuits out of the building would not be cost effective.

 

[iwire]

Re: Power poles

I can think of no way to apply the tap rules for this that would save you money.

You would have to provide OCP at each receptacle.

IMO Wayne is on the money, a centrally located panel(s) is the best way to go.

I would be concerned with voltage drop on the branch's and the feeder though.

Luckily you know the loads so you can do the calculations and be sure you have covered yourself.

If the customer thinks this will be a cheap job they are in for a surprise.

I would imagine a place like this would have 3 phase, if not what is the service?

You are talking about adding 500 amps at 120 volts, 250 amps at 240.

If you have 3 phase one 225 amp 3 phase feeder with a double tub panel (225 amp main in the first one, feed through lugs to the MLO second panel) should cover this load. Not much room for expansion though.

I come up with about 167 amp per leg and the 225 feeder allows for 180 amps continuous.

Depending on the distances involved it might make sense to make the feeder 480 volt if available and have a transformer at the panel.

At one processing plant we work at that is how we handle all the 120 volt heat trace circuits.

Close to 500 120 volt circuits of 20 and 30 amps each running 24/7.

[ October 20, 2003, 06:11 AM: Message edited by: iwire ]

 

[sjaniga]

Re: Power poles

Hurk,

But will all 50 have a load on them at the same time?

Yes, these units do not have thermostats to turn on and off. Once plugged in they are on full power, this is why the customer wants them on timer/contactors to save on electric bills.

Iwire,

If the customer thinks this will be a cheap job they are in for a surprise.

Yes the customer just about fell over when he got the cost. Our first quote gave prices of 50 circuits from the electric room out to the trucks.
Our second quote was to install the panels outside to cut down on pipe and wire costs, this too was stunning to the customer. We even discussed using only 25 circuits with reversing contactors so half could be on for awhile then the other half, and never on at the same time but the customer doesnt think it would work for this application.

In the end the customer does not want the panels outside, this is why I came here for some info.

Oh, and yes we did account for derating and voltage drop. It looks as if we have covered the bases.

Thanks again,
Scott

 

[tom baker]

Re: Power poles

We have an installation at fire stations with block heaters in the fire trucks being on all the time. We had a 20 Amp cord cap with strain grip that the fire truck plugs into. When the truck leaves it unplugs itself. What we have noted is the 20 amp cord cap overheats due to the 1500 watt block heater being on all the time. We have to replace the cord caps every six months.
We solved the problem by going to a 240 volt block heater, with thermostat.
See if the trucks can be set up with 240 or 208 volt block heaters, and the block heaters with thermostat.

 

[sjaniga]

Re: Power poles

Tom, thanks for the reply, I contacted the heater manufacturer this morning to find out that these units cannot be changed due to the fact that they have small oil circulating motors also.

The MFG did say we could order new ones at 208v.

Problem is that it is already starting to get cold at night here in MI, so we are stuck with our first plan.

Scott

 

[tom baker]

Re: Power poles

What if you used a contactor to turn on and off banks of receptalces? Then you would have loads that are not energized at the same time, and the load calc would be reduced.
Are the trucks parked outside, outside under a cover or inside?

 

[sjaniga]

Re: Power poles

Tom, we did suggest to use reversing contactors to turn the first 25 trucks on for a period of time then switch over to the other 25.

Problem is that the Mfg suggests that to work properly these heaters need to be on for 3 hours
continuous, they say that intermitant switching will reduce the temp of the block.

Personally I would cycle the recepts also. No need now that the customer understands the cost issue and has accepted it.

Scott

 

[don_resqcapt19]

Re: Power poles

What about a product like this? It has 2 breakers and 2 receptacles so you would use one for two trucks. The line terminal block is set up for a loop feed and can accomodate two #2 thru 250 kcmil.
Don

[ October 20, 2003, 03:55 PM: Message edited by: don_resqcapt19 ]

 

[earlydean]

Re: Power poles

I like that. Such a product could be assembled on the site, a 100 amp, 2 circuit panel runs about $25. Run four loops of #2s. Feed through contactors, controlled by a time clock.