Bus power from a venue

[Lsly]

Hello all,

I'm wondering what guidelines there might be for installing bus power for a venue to the bus. We have always just provided a 50amp 250v 3 wire plus ground service. Now engineers are wanting GFCIs. This of course goes against what many of us understand about RVs and Busses and their systems. They actually installed a service and were confused as to why it's was tripping regularly.

Anyway, I feel that a sub panel then the branch circuits would be best. Any thoughts or systems that are compliant and working well? Code references are very helpful. As you can imagine there is no clear answer.........

Thanks
LSly

 

[DrewE]

Here's a pertinent article. Receptacles for power feeds for RVs and mobile homes above 20A/120V are specifically exempted from requiring GFCI protection in the 2020 NEC (and, I believe, were not required to be so protected in previous revisions of the code as receptacles above 20A were not generally required to have GFCI protection in any typical case). Article 551.71 F is the specific code citation for RV parks.

My personal opinion is that GFCIs for RV receptacles make a lot of sense, even though they aren't required, as I suspect most cases of them tripping "at random" are actually due to faults in RV wiring that were lying latent: neutral/ground faults, possibly from miswired transfer swtiches; leaky heater elements in absorption fridges or in water heaters; water intrusion; or that sort of thing. I have not done extensive or non-extensive studies on the matter, though, and could be wrong. There are some situations where benign and reasonably expected leakage current from RFI filters on devices and from wiring capacitance or inductance could exceed a normal GFCI trip threshold, but to my guestimation they seem rather unlikely in most cases.

As I understand things, the typical way campgrounds are wired is to have a single rather large circuit (200A or so) feeding several sites, with typically preassembled RV power pedestal boxes connected to this feeder. Each box has rated breakers and 50A, 30A, and 20A receptacles--or possibly just 30A and 20A if it's not a 50A site. If I were wiring up receptacles for entertainment busses, I'd use these boxes and a similar overall approach.

(Incidentally, it is entirely permissible per the NEC for a 50A RV site to be fed from two phases of a 120/208 three phase system, in addition to the much more usual 120/240 split phase.)

 

[MNicolai]

Here's an article from Mike Sokol on that matter, who I would consider eminently qualified in this matter. This echoes the article that @DrewE just linked too.

Mike's opinion is generally that GFCI's are great on 20A circuits but on 30A and 50A circuits there's too much permissible leakage current for the GFCI's to avoid false trips and ultimately could lead to people lifting grounds and creating more dangerous circumstances. He would rather see GFCI's on individual circuits within the RV than upstream on a feeder circuit where those various leakage currents can sum together and cumulatively produce false trips.

 

[ACTSTech]

Road house where I frequently work got some pushback from the Fire Marshall over not having GFCIs on their posts because it’s a “potentially wet” area. Electrician popped a GFCI breaker in at the panel instead and the fire Marshall said good enough. Probably best to check local code though.

 

[Footer]

The only shore power we have is inside our dock where its dry, but for us its just 14-50 connectors straight to a standard breaker. Our outside parking area we let generators run. We have fire marshals, engineers, and whatever around all the time and they have never brought up the GFCI thing. The buses do have protection... let them use it.

 

[Lsly]

Thanks everyone. Much of the answers go along with my research and are much appreciated.

 

[TimMc]

Hello all,

I'm wondering what guidelines there might be for installing bus power for a venue to the bus. We have always just provided a 50amp 250v 3 wire plus ground service. Now engineers are wanting GFCIs. This of course goes against what many of us understand about RVs and Busses and their systems. They actually installed a service and were confused as to why it's was tripping regularly.

Anyway, I feel that a sub panel then the branch circuits would be best. Any thoughts or systems that are compliant and working well? Code references are very helpful. As you can imagine there is no clear answer.........

Thanks
LSly

Buses and RVs have generators, shore power connection, and likely a battery bank feeding an inverter. The ground/neutral bonding is handled differently because the generator and inverter are considered "separately derived services" in Code. It's possible that the transfer switches in the bus are not set up to re-assign the neutral bond when on shore power, and that's what tripping a GFCI.

Have the engineers look at Code for RV parks, as that's the "occupancy". Shore power is not "for use by personnel" and a GFCI is not required. If they get all bent over the 20 amp outlet, it can be protected by a GFCI breaker.

 

[RickR]

There is a movement afoot to require GFCI for RVs. Apparently it's been delayed due to high costs.
https://rvbusiness.com/arvc-secures-gfci-amendment-aids-park-owners/