Mobile Home Park Electrical System wiring

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zemingduan

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Philadelphia,PA
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Electrical Designer
Hi guys. I am now working on the electrical design of a mobile home park design. They have 24 new mobile homes added to the existing electrical system. 8 mobile homes in a row. We need to design the wiring for these new mobile homes. Our proposal is to feed each 8 mobile homes from one 250A breaker on the MDP(The load is calculated per NEC 550). The underground conductors will daisy chain the 8 mobile homes service equipment(see sketch below). The wire length will e around 260 feet. We will consider the voltage drop when sizing the conductors. I didn't see any code issues or violations for this design. All the underground conductors that daisy chain the mobile home can be considered protected by the 250A breaker. What do you think? Do I miss any requirements? What is your typical wiring for a mobile home park electrical system? Thanks!

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Hi guys. See below for my load calculations. The demand load for each mobile home is 91A per 550.18. 550.31 permit a 0.28 demand factor for 8 mobile homes. I think per the wording of 550.31, you can apply this demand factor like this: 91x8x0.28 A = 204A.

Or am I wrong? You can't apply the demand factor to the demand load calculated per 550.18(91A), since the load calculated by 550.18 is already a demand load after applying some demand factor. Should you apply the demand factor 0.28 in a way similar to 220.84 calculations for multifamily dwelling?
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kwired said:
seems ok for no more than we know what you have.

I think the fridge can be included with the SABC's
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Thanks kwired. But why does code allow you to apply 0.28 for 8 mobile homes and allow you to apply this demand factor to the calculated total demand load rather than the total connected load of mobile home? This will result in a huge reduction in the service comparing to the 8 multi-family dwelling units. You need to apply 0.43 to the total connected load of 8 dwelling units per 220.84. In the same condition, 8 all electrical(elec. range, water heater, HVAC, washer) dwelling units usually need a 400A 1phase service. I feel like most mobile homes functioned as a permanent dwelling and there is no much difference with multi-family dwelling units. This big difference in the required service between 8 mobiles homes and 8 units in a multi-family dwelling sort of doesn't make sense to me.
 
hillbilly1 said:
The 3va per square foot is not realistic anymore, due to the advent of LED lighting it is much lower than that now.
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Yes. Much agree with this. But you still have to calculate it per CODE for the worst case :cry: . Don't know will NEC modify this or add some exceptions in the future.
 
hillbilly1 said:
The 3va per square foot is not realistic anymore, due to the advent of LED lighting it is much lower than that now.
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But it includes general use receptacles as well as lighting, so realistic value may not be ~25% of that 3 VA (presuming LEDs' consume ~25% of an equivalent incandescent).
 
zemingduan said:
Thanks kwired. But why does code allow you to apply 0.28 for 8 mobile homes and allow you to apply this demand factor to the calculated total demand load rather than the total connected load of mobile home? This will result in a huge reduction in the service comparing to the 8 multi-family dwelling units. You need to apply 0.43 to the total connected load of 8 dwelling units per 220.84. In the same condition, 8 all electrical(elec. range, water heater, HVAC, washer) dwelling units usually need a 400A 1phase service. I feel like most mobile homes functioned as a permanent dwelling and there is no much difference with multi-family dwelling units. This big difference in the required service between 8 mobiles homes and 8 units in a multi-family dwelling sort of doesn't make sense to me.
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IDK. looking at 550.18, it is similar but not the same as art 220 calculations for a dwelling. One of first things I noticed is in (A)(5) - first 3000VA @ 100%, remainder @ 35%.

220.82 says first 10,000 VA @ 100% and the rest at 40%. I see your calculations say that is what you used, but 550.18(C) says you can use 220.82.

If you used 550.18(A) instead of 220.82 (leaving the fridge in there though I still think it is already accounted for in SABC's) you would have 9881 instead of 15064 for your general total demand.

Why said "dwelling" can have less demand than a dwelling that is not also a mobile home (even if they have basically the same loads) I have no clue.
 
kwired said:
IDK. looking at 550.18, it is similar but not the same as art 220 calculations for a dwelling. One of first things I noticed is in (A)(5) - first 3000VA @ 100%, remainder @ 35%.

220.82 says first 10,000 VA @ 100% and the rest at 40%. I see your calculations say that is what you used, but 550.18(C) says you can use 220.82.

If you used 550.18(A) instead of 220.82 (leaving the fridge in there though I still think it is already accounted for in SABC's) you would have 9881 instead of 15064 for your general total demand.

Why said "dwelling" can have less demand than a dwelling that is not also a mobile home (even if they have basically the same loads) I have no clue.
Click to expand...
In 220.82 the general load includes lighting,SABC, appliances and range. But in 550.18(A) it only includes lighting and SABC, laundry.
 
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