Mobile Home Service size

[tbassler_99]

I am working on a mobile home park with an existing 8-unit meterbase that the owner modified. They added a 100A disconnect and feeder to a small house (NEC demand 85 amp). The county is asking for load calculations and a one-line diagram.

The electrician sent me a sketch of the meterbase.

There are four 50 amp 2-pole breakers, three 100 amp 2-pole breakers and one 60 amp 2-pole breaker. It looks like all feeders are #6 Al.

I have never designed or worked on a trailer park before.

i started with the load calculations. NEC 550.31 says park wiring system shall be a minimum of 16,00 VA per lot. @ 240V I get 67A. Using 310.15(B)(7) 83% rule I get 55 amps.

How is any lot fed with a 50 amp feeder? I looked all over the code, internet, Annex D, etc. I can't get past the first step.

i have done many hotels and multi-family housing units but this has me stumped.

Can anybody point out my obvious oversight?

Thanks

 

[Little Bill]

Bump

 

[ptonsparky]

How old is this park? Older mobile homes only had 60 amp service.

 

[kwired]

I am working on a mobile home park with an existing 8-unit meterbase that the owner modified. They added a 100A disconnect and feeder to a small house (NEC demand 85 amp). The county is asking for load calculations and a one-line diagram.

The electrician sent me a sketch of the meterbase.

There are four 50 amp 2-pole breakers, three 100 amp 2-pole breakers and one 60 amp 2-pole breaker. It looks like all feeders are #6 Al.

I have never designed or worked on a trailer park before.

i started with the load calculations. NEC 550.31 says park wiring system shall be a minimum of 16,00 VA per lot. @ 240V I get 67A. Using 310.15(B)(7) 83% rule I get 55 amps.

How is any lot fed with a 50 amp feeder? I looked all over the code, internet, Annex D, etc. I can't get past the first step.

i have done many hotels and multi-family housing units but this has me stumped.

Can anybody point out my obvious oversight?

Thanks

Your question is valid. Though you can have a 50 amp feeder to an individual home, and an exception even can allow a 40 amp feeder, the park wiring must still have at least 16000 VA capacity in feeder to each lot. I see that as meaning you need 67 amp conductor, and 67 amp or more overcurrent device on the park feeder. For service load calculations however you could have less load when applying allowable demand factors, but those demand factors only apply to service or common feeders not to a feeder supplying only one unit.

So if you have 8 mobile homes and no load details (maybe you laying out the park but have no mobile homes yet) you should be able to calculate minimum service needed to be 16kVA x 8 = 128kVA x .28 (from table 553.31) = 35.84 kVA. Might get you into trouble if you use that for service and end up with much for electric heat or water heating in units that arrive, but that would be a minimum if you didn't have unit details.

 

[tbassler_99]

Your question is valid. Though you can have a 50 amp feeder to an individual home, and an exception even can allow a 40 amp feeder, the park wiring must still have at least 16000 VA capacity in feeder to each lot. I see that as meaning you need 67 amp conductor, and 67 amp or more overcurrent device on the park feeder. For service load calculations however you could have less load when applying allowable demand factors, but those demand factors only apply to service or common feeders not to a feeder supplying only one unit.

So if you have 8 mobile homes and no load details (maybe you laying out the park but have no mobile homes yet) you should be able to calculate minimum service needed to be 16kVA x 8 = 128kVA x .28 (from table 553.31) = 35.84 kVA. Might get you into trouble if you use that for service and end up with much for electric heat or water heating in units that arrive, but that would be a minimum if you didn't have unit details.

Thank for your response. I was getting self conscious since there were lots of views and no responses. It is an old park. I thought that requirement was just for the feeder to the meterbase. Using 16,000 VA for seven lots and my calculated 19.6 kVA for the house, and the 0.28 demand factor for 8 lots per 550.32 I get 154 Amps demand.

I am just worried about the 50A services to existing lots. Besides the obvious violations: 100A breaker feeding #6 Al, #6 Al feeding the new house with 83AA demnd load. I know how to deal wit hthat, Its the 50A feeder to the trailer I cant figure out.

i cant reach the master electrician right now, but i will update this post with my findings.

Thank you all again

 

[kwired]

Thank for your response. I was getting self conscious since there were lots of views and no responses. It is an old park. I thought that requirement was just for the feeder to the meterbase. Using 16,000 VA for seven lots and my calculated 19.6 kVA for the house, and the 0.28 demand factor for 8 lots per 550.32 I get 154 Amps demand.

I am just worried about the 50A services to existing lots. Besides the obvious violations: 100A breaker feeding #6 Al, #6 Al feeding the new house with 83AA demnd load. I know how to deal wit hthat, Its the 50A feeder to the trailer I cant figure out.

i cant reach the master electrician right now, but i will update this post with my findings.

Thank you all again

What about it can't you figure out? If it is cord and plug connected (which some with minimal load can be) they are a 14-50 plug/receptacle. Most I have ever seen past 30 years have required 100 or if they have electric heat usually a 200 amp feeder, but have seen a few older ones with a 50 amp cord and plug, those usually have all gas heating appliances.

 

[tbassler_99]

What about it can't you figure out? If it is cord and plug connected (which some with minimal load can be) they are a 14-50 plug/receptacle. Most I have ever seen past 30 years have required 100 or if they have electric heat usually a 200 amp feeder, but have seen a few older ones with a 50 amp cord and plug, those usually have all gas heating appliances.

They are all hardwired.

What I couldn't figure out is that 550.31 requires park electrical wiring systems shall be calculated at a minimum of 16,000 VA per lot or use 550.18. at 240V Thats 67 A. I thought that would require a minimum of 60A feeder.


I don't know if the code has changed, but all those 50A feeds were approved when it was installed, so I will just worry about the meterbases and the existing wiring.

The electrician is going up there today and verifying what meter goes to what lot, wire size for the the new feed to the house (lot 114), date of installation, etc.

AS you can probably tell, I am not an electrician. I already messed up. when the electrician said #6 THW wire, he thought I would know it is copper. I didn't.

My calc for the demand load for the 8-meters is 154A.
7*16,000 VA +19,646 VA=36,861 VA. = 154 a @240v.

so I will just make sure all feeders and breakers match, all meterbases are updated to the new utility (XCEL) standards and I should be good.

Thanks again for your assistance. I will update with my final findings and resolution in few days.

 

[kwired]

When it was new the 50 amp to existing lots may have been plenty of power regardless of what may or may not have changed code wise. They likely had gas heat, gas water heating, gas range, gas dryer, probably not all that large of homes and maybe actual load hardly ever exceeded 30 amps. Today it might still hold on 50 amp main, but maybe gets close to tripping it on occasion.

 

[tbassler_99]

It got a permit

It got a permit

I promised to follow up and I apologize it took me so long. First of all, thanks everyone for enlightening me.

This whole job started because they installed a new house on a lot and upgraded the meter to 100A, installed the new service and then applied for a permit.

The electrician set up a meeting with XCEL Energy, the Boulder inspector, someone from the trailer court. I didnt even make me the meeting. The electrician showed the inspector my calculations on unstamped preliminary drawings and the job was approved, and the new residents moved in.

Even with the code violations the electricians documented on his as-built. The inspector only cared about the existing 200 amp feed to the meter base.