I'm a journeyman electrician with much industrial etc. experience however, no mobilehome experience. I'm currently assistant manager of a 192 unit mobilehome park and do most of the electrical if I can handle it on a part time basis. I've read article 550 and constantly refer to it. All homes are double wide. Main power distribution consists of 3-600 amp Nema 1 distribution panels,all with many 100amp 2pole breakers feeding multiple units with 1/0 typw UF al conductors. All feeders are direct burial(no conduits). All units have 50amp main breakers. Over the years(before my time) many units have been "piggybacked off of other pedestals because(I think of opened feeders from the main distribution panel),Some jumpers between pedestals are single wire, some are multiple wire . I have a low voltage problem at some units because of to many units on 1 main feeder. How many uinits can you put on 1-100amp feeder, as a general rule? Also, I need to change many pedestals and am having a hard time finding manufactuers. The only one I have found so far is Milbank and they are expensive.Any suggestions? Also, I see the grounding conductor at each unit going down into the ground but no sight of ground rods. Is there some "trick to the trade" for grounding these pedesatals. or is the ground rod below the surface? Any help would be greatly appreciated.
Well, lets back up, and look at this as we would any other service. I can't really argue code, and code may very well allow for multiple answers...so just bear with me as I "think out loud."
The 600 amp panels are your actual "service" location, so the ground rod should be there. There ought to be a suitably sized ground wire run from there, out to the pedestals. Multiple pedestals can "share" the same ground wire, I would think.
Now for wire sizing, and over-current protection. 100 Amp breakers? Aluminum wire? 1/0 is the minimum size allowed by table 300-16- and that table doesn't allow for voltage drop over the length of the run.
Jumpers between pedestals? Sounds like you've got some problems, some 'broken bones' with 'band aids' on them.
Now, two factors affect voltage drop; the distance, and the load. I'd first take amp readings at the panel, and see just how many amps are being drawn. If the 1/0 is drawing only 70 amps, well, your problem lies elsewhere. If it's drawing 110 amps, well, you need "more power." (Bigger wire, more circuits, etc).
Then there is the matter of voltage itself. With all power "off," how many volts is the PoCo giving you? A big difference between the 'load' and 'no-load' voltages suggests that maybe the PoCo needs to make some changes on their side of the meter.
Pedestals expensive? Sure- but nothing lasts forever. You might start planning to completely re-do your park, one section at a time. Besides replacing the pedestals, you might want to replace the buried wire and change your distribution pattern.
It's not unknown for a 30 space park, over the years, become a 100 space park. This, as well as the trend of us using far more power than we did in the past, will eventually exceed the capacity of the system.
Re: Mobilehome power distribution#97805 03/23/0611:02 PM03/23/0611:02 PM
Reno 550.32 requres a ground electrode at each "disconnecting means" in sight and within 30 ft of the mobile home. (the pedestal). When I was with the state we did a lot of these. You are right about the power. Assume the worst about the load. The end up with huge HVAC loads in the south since these homes have little insulation and the sun load is worse than a house. (no attic) We ended up replacing the standard 50a pedestals with 100a services if it was anything larger than an old single wide.