Choosing panels and equipment based on load calcs.

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Electron_Sam78

Electron_Sam78

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Palm Bay, FL
I've got a few services I need to install and I've come up with load calculations 360 and 378 amps (2 different services). Would this be a 400 amp service? I think I've heard that panels and meter cans and such are rated for 80% so a 400 amp panel could only take 320 amps? Does that mean I'd have to move up to a 600 amp service as far as panels and meter boxes? What about the main breaker? That can still be a 400amp right? Please give NEC references with answers if you can.
 
Yes, 400-amperes is fine. A 400-ampere meter socket is rated for 320 continuous amperes. The continuous loads are already figured into your load calculation as required in Article 220.
 
When you did your calculations, did you factor in the continuous loads (e.g. multiply them by 125%)? If so, you're fine as your result will be the value you need.

A panel bus or meter itself could probably even take the full current continuously (although I have no proof and have seem some panels say 200 continuous amps and others just say 200 amps). It is the breakers that cause this 80% rule. I'm not sure about a meter can except that the 320/400A ones usually say "400A, 320A continuous".
 
These are calculations for an RV park and were calculated per article 551. Any specific loads, including continuous, are unknown but each pedestal (I have 3 sets of 20 and 1 set of 21) was calculated at 9600VA per section 551.73 and demand factors applied per T551.73.
 
Electron_Sam78 said:
These are calculations for an RV park and were calculated per article 551. Any specific loads, including continuous, are unknown but each pedestal (I have 3 sets of 20 and 1 set of 21) was calculated at 9600VA per section 551.73 and demand factors applied per T551.73.
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Sam,

3 sets of 20
1 set of 21

81 x 9600 = 777600

777600 / 240 = 3240a

Demand Factor of 41% = 1328.4a Calculated load?

Where did I go wrong here ?
 
I'm going to have 4 separate services. This is for a whole camp ground with spaced out loops.

20 @ 9,600VA each(3 sets) = 192,000VA * .45 = 86,400VA / 240V = 360a
21 @ 9,600VA each (1 set) = 201,600VA * .45 = 90,720VA / 240V = 378a

I could do it your way then split it 4 ways I guess. I'm not really sure. I'm new to RV parks. The NEC is unclear about how to calculate in such an instance. It just says the demand factor applies if there are so many sites. I'm assuming you'd use the demand factor for however many sites you're going to have on each service from the POCO.

The entire recreation area actually has 4 camp grounds with about 500 camp sites. I'm going to become intimately familiar with RV parks!
 
Be carefull. Campers on a hot summer day = lots of AC that might never shut off in daytime. Many have microwaves and such. If you cut this too close you will be in a mess. Your second guessing actual use. Give you a hint if i am camping and electric is included i crank mine to the max while out at the pool. Dont forget the number of required 50 amp 2 poles
 
Jim W in Tampa said:
Be carefull. Campers on a hot summer day = lots of AC that might never shut off in daytime. Many have microwaves and such. If you cut this too close you will be in a mess. Your second guessing actual use. Give you a hint if i am camping and electric is included i crank mine to the max while out at the pool. Dont forget the number of required 50 amp 2 poles
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These are all 50 amp pedestals (9600VA each per 551.73) with a 30 amp receptacle and a 20a GFCI.

Any suggestions on how to account for hot days and packed out sites? How would you know how much to increase the ampacity with so many unknowns? We do have information from other sites we can take into consideration. We have one loop that has 41 50a/30a combo pedestals that was 99 percent full on a day that was 97 degrees with a heat index of about 105. The loop kept tripping the main 400a CB after about 3 o'clock. Amp readings, after it was reset, showed around 280a on one leg and 480a on the other. It tripped an hour later so I don't know what the load was leading up to the trip but I hooked a recording meter to it today so we might know something better tomorrow or the next day. (I know, quite an imbalance! We have since gone around and balanced the load of the 30a receptacles by alternating legs in the pedestals - much more balanced today!) About 75% of the load is from single leg 30a RVs and about 20% comes from 2 leg 50a RVs. I'm not sure what it would look like with 75% 50a RVs...
 
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Electron_Sam78 said:
These are all 50 amp pedestals (9600VA each per 551.73) with a 30 amp receptacle and a 20a GFCI.

Any suggestions on how to account for hot days and packed out sites? How would you know how much to increase the ampacity with so many unknowns? We do have information from other sites we can take into consideration. We have one loop that has 41 50a/30a combo pedestals that was 99 percent full on a day that was 97 degrees with a heat index of about 105. The loop kept tripping the main 400a CB after about 3 o'clock. Amp readings, after it was reset, showed around 280a on one leg and 480a on the other. It tripped an hour later so I don't know what the load was leading up to the trip but I hooked a recording meter to it today so we might know something better tomorrow or the next day. (I know, quite an imbalance! We have since gone around and balanced the load of the 30a receptacles by alternating legs in the pedestals - much more balanced today!) About 75% of the load is from single leg 30a RVs and about 20% comes from 2 leg 50a RVs. I'm not sure what it would look like with 75% 50a RVs...
Click to expand...

Was going to suggest you rotate. Problem is everything on campers is 120 and depending on mfgr hard to know what leg they put the AC and the power inverter. Also in a case where the main triped you likely have all the campers overheated and would need to turn 1 at a time back on because they all will be starting. Do not know of any method to get real number other than simply over kill. When we camped i had a 34 foot pace arrow with 2 roof top units. Rewired so both could run at same time on 30 amp single. Am sure i was major load. Wish you best of luck. Would design it so that its easy fix to add an extra service if it proves to be undersized. On hot days i would not count on the AC not being cont. load and would take it at 125%
 
Good points Jim. It might be a good idea to put the service in the middle of the loop

in case you need to increase it in the future.
 
Jim W in Tampa said:
Was going to suggest you rotate. Problem is everything on campers is 120 and depending on mfgr hard to know what leg they put the AC and the power inverter. Also in a case where the main triped you likely have all the campers overheated and would need to turn 1 at a time back on because they all will be starting. Do not know of any method to get real number other than simply over kill. When we camped i had a 34 foot pace arrow with 2 roof top units. Rewired so both could run at same time on 30 amp single. Am sure i was major load. Wish you best of luck. Would design it so that its easy fix to add an extra service if it proves to be undersized. On hot days i would not count on the AC not being cont. load and would take it at 125%
Click to expand...

Do you have a 50a plug in on your RV?
 
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