I have a question for all the ABYC experts here.
According to E-11 (2003 version), if a boat
has two shore power
inlets (in my case, two 30A 3-wire services), then the neutrals must not be connected together on the boat
- they must be kept separate.
Not a problem - yet. I'm assuming that keeping them separate assures that there will still be only one point - back at the dock service
point - that each safety
ground is connected to its associated neutral only at that single
point. I get that.
My plan was to feed the two AC services from shore and the genset's two outputs (L1 & L2) via a transfer switch to the main panel - which has all the high-load AC appliances
- water heater
, A/C, auxilary battery
chargers, and the inverter
. I don't have any 240V appliances
, but I want that option for future use (maybe a dive compressor
The problem is my Magnum Energy MS2812 inverter
. It has the nice capability of passing through not only one, but two, AC service
circuits (L1 & L2) when in charging
mode. Of course, when in invert mode, the neutral is internally tied to the ground - which is normal. The two hot outputs are internally bridged when inverting, so you have only 120V service (they do have a larger model 4024 which can support 120/240 output when inverting).
The inverter would in turn feed the low-load sub-panel - again with two AC services (L1 & L2).
However, note that I said "neutral" and not "neutrals". The unit supports only a single
Neutral in, and a single Neutral out. Which is fine if I'm running a four-wire 120/240 50A split-phase system. But the marine
electrician convinced me early in the project
that I'd have load balancing problems, and recommended that we go with two 30A shore power
inlets. Now I'm stuck... Both the main AC panel and the subpanel currently support a single hot side (although they could be modified somewhat)...
I just got off the phone
with Magnum's tech support, and the guy I spoke with didn't think it would be a problem to tie the neutrals of the two shore power services together - as long as the marina's system was correctly wired. All bets are off if it's not.
My question is - what am I risking if I connect the neutrals together at the inverter?
Or should I just have the inverter feed the subpanel with just one circuit - and possibly risk having the two service "unbalanced" - just what the electrician wanted to avoid in the beginning. If I went with a single 50A 4-wire shore power inlet, I wouldn't have this problem - only one neutral to deal with (just like the genset)...
The long term plan is for the genset to do most of the heavy lifting (supplemented by a wind generator
panels). Docks will be few and far between while cruising.
I could include a couple drawings if that would make it a bit clearer...