RV Park Feeder Question

[jumper]

I agree with this.
I even called the power company once to ask how they would calculated the load on RV Outlets and they indicated without knowing what was going to pull up, they calculate at 100%.

They would calculate a 100 amp feeder to a pedestal with a 50 amp 30 amp and a 120v GFI in it.

I know the 50 and 30 are in the pedestal for convienience, but, if there there, by rights there should be enough power run to the pedestal to service all receptacle outlets in the pedestal.

That would include enough power to run the 50,30 and 120v gfi all at the same time.

I would call that a good design practice. I do not believe, however, that it is a code requirement.

Jap, it is not required.

Where the electrical supply for a recreational
vehicle site has more than one receptacle, the calculated
load shall be calculated only for the highest rated receptacle.

 

[jap]

I agree its not required.

 

[jumper]

Okay, now back to 9600 VA.

You can use this if you supply the 50 amp receptacle with a 40 amp feeder and OCPD, per Table 210.21(B)(3), but I still say that if it is a 50 amp supply OCPD, the feeder must be good for 50 amps unless you can show the actual load is less and use 240.4(B).

 

[charlie b]

. . . but I still say that if it is a 50 amp supply OCPD, the feeder must be good for 50 amps unless you can show the ACTUAL load is less and use 240.4(B).

Allow me to offer a different way of saying this. If it is a 50 amp supply OCPD, the feeder must be good for 50 amps unless you can show the CALCULATED load is less and use 240.4(B). And since the NEC allows me to calculate at 9600, I should be able to base my decision on the reuse of the existing wire on that value.

In actual practice, this may turn out to be a non-issue. If the number of CCCs in any given conduit is less than 10 (i.e., maximum of four sites served via any given conduit), then the wire's ampacity will be above 50. But I won't know for certain until I get a chance to see all the handholes in the RV Park's distribution system.

 

[cpinetree]

Ground wire?

Ground wire?

You say that each pedestal is fed with 3 wires, shouldn't each pedestal have 4 wires? (hot-hot-neutral-ground).

I think the 50 amp recpts are 240v and the 20 + 30 amp 120v, no?

 

[jumper]

Do the math for the other RV outlets, there is no reduction in VA.

(A) Basis of Calculations. Electrical services and feeders
shall be calculated on the basis of not less than 9600 voltamperes
per site equipped with 50-ampere, 208Y/120 or
120/240-volt supply facilities; 3600 volt-amperes per site
equipped with both 20-ampere and 30-ampere supply facilities;
2400 volt-amperes per site equipped with only 20-
ampere supply facilities.

 

[Sierrasparky]

Do the math for the other RV outlets, there is no reduction in VA.

(A) Basis of Calculations. Electrical services and feeders
shall be calculated on the basis of not less than 9600 voltamperes
per site equipped with 50-ampere, 208Y/120 or
120/240-volt supply facilities; 3600 volt-amperes per site
equipped with both 20-ampere and 30-ampere supply facilities;
2400 volt-amperes per site equipped with only 20-
ampere supply facilities.

Based on that I think it's good to go with the existing feeder.

 

[jumper]

Based on that I think it's good to go with the existing feeder.

A 50 amp 240v receptacle on a 40 amp circuit shall be calculated at not less than 9600 VA.

A 30 amp 120v receptacle on a 30 amp circuit shall be calculated at not less 3600 VA. 240v changes the VA.

A 20 amp 120v receptacle on a 30 amp circuit shall be calculated at not less 2400 VA. 240v changes the VA.

 

[Sierrasparky]

A 50 amp 240v receptacle on a 40 amp circuit shall be calculated at not less than 9600 VA.

A 30 amp 120v receptacle on a 30 amp circuit shall be calculated at not less 3600 VA. 240v changes the VA.

A 20 amp 120v receptacle on a 30 amp circuit shall be calculated at not less 2400 VA. 240v changes the VA.

Oh so are you saying that the combined 3 oultets must be calculated for a total of 15.6 kw? I don't see all three being used at one time at a single rv spot. it is a either or deal. I see no issue of over wiring the place the owner need to be aware.

 

[jumper]

Oh so are you saying that the combined 3 oultets must be calculated for a total of 15.6 kw? I don't see all three being used at one time at a single rv spot. it is a either or deal. I see no issue of over wiring the place the owner need to be aware.

No, I am saying that you cannot use 9600VA for a 50 amp receptacle on a 50 amp circuit. Maybe for the service or service feeder, but not to a pedestal. You cannot put a 49 amp load on a conductor that is rated for 47.5 amps.

 

[Sierrasparky]

No, I am saying that you cannot use 9600VA for a 50 amp receptacle on a 50 amp circuit. Maybe for the service or service feeder, but not to a pedestal. You cannot put a 49 amp load on a conductor that is rated for 47.5 amps.

Ok I think I got it!

 

[jumper]

No, I am saying that you cannot use 9600VA for a 50 amp receptacle on a 50 amp circuit. Maybe for the service or service feeder, but not to a pedestal. You cannot put a 49 amp load on a conductor that is rated for 47.5 amps.

Now that I think about, I think you still need to use 12kVa for a 50 amp circuit and then apply the demand factors to the service calc.

 

[jumper]

I guess I am wrong, not one member agrees.

 

[charlie b]

You say that each pedestal is fed with 3 wires, shouldn't each pedestal have 4 wires? (hot-hot-neutral-ground).

You are right. The green wires are there as well. But since they were not relevant to my question, I didn't bother to mention them.

I think the 50 amp recpts are 240v and the 20 + 30 amp 120v, no?

You are right again, at least about the 20s and 30s. But I am thinking that the 50's are 120/240, not just 240.

 

[charlie b]

Now that I think about, I think you still need to use 12kVa for a 50 amp circuit and then apply the demand factors to the service calc.

Keep in mind that the wires from the panel to the pedestals are feeders, not branch circuits. I am calculating a feeder load, and the NEC says I can calculate the feeder to a 50-amp at 9600 VA. It also says that I only have to calculate the largest of the available outlets, so I can ignore the 30 and the 20.

I see this as akin to calculating duplex receptacle outlets at 180 VA each. That equates to 1.5 amps, and we all know that vacuum cleaners, hair dryers, and other loads that draw way more than 1.5 amps will be plugged into those outlets.

 

[charlie b]

I want to thank you all for your contributions to this thread. But I must mention that I am about to depart on a week long business trip. So I won't be participating in any other discussions on this topic.

Regards,
Charlie