Bridging Heat Pump Across Two Circuits

[prroots]

We recently purchased a used Beneteau 411 which came with two 30 amp shore connections. Connection 1 powers all standard AC loads including battery charger, water heater, AC outlets, microwave, and AC lights. Connection 2 powers two heat pumps via separate circuit breakers. We have just signed up for a marina slip which will have a single 30 amp supply. We wonder if we can install a switch or circuit breaker to bridge one of the two heat pumps into the standard circuit. Obviously, we would then have to limit loads to avoid exceeding the 30amp limit. Is this idea otherwise viable? Suggestions or comments appreciated
Pete

[twistedtree]

Yes, you could just move the breaker over to the other 30A circuit. But before doing that I'd suggest checking the power draw of th eother high power appliances to sort out how effectively you can avoid nuisance tripping of the main 30A breaker.

[prroots]

Originally Posted by twistedtree

Yes, you could just move the breaker over to the other 30A circuit. But before doing that I'd suggest checking the power draw of th eother high power appliances to sort out how effectively you can avoid nuisance tripping of the main 30A breaker.

Thanks. I didn't make myself clear. I still want the option of feeding both heat pumps off connection 2 since if 50A is available I have a Y connector that feeds both inputs simultaneously.

Also, seems I might need a double pole, double throw switch so that the heat pump can be connected to circuit 1 or 2, but never both simultaneously. I'm thinking that there could be a serious problem if the heat pump is simultaneously fed by both inputs
Pete

[Dsanduril]

This approach is entirely viable. I think your own suggestion of double-pole double-throw is probably the best, it will force you to keep C1 and C2 separated.

In theory there is no big deal in joining C1 and C2 together if they are fed from the same source and use the same phases. Since you won't have any control of that... I've wired a bunch of marinas, most of them are wired with 208V 3-phase Wye connected transformers. Then each slip is fed 120V from that service. If you plug in two connections you will have no way of knowing if they are on the same phase (well, you could with the right meter or by checking out the wiring). Generally, an electrician would wire nearby circuits from separate phases to try and spread the load evenly on all three phases. You don't want to have to worry, when plugging in your two connections, about making sure they are on the same phase because you have them cross-connected inside the boat.

If you're getting 240V single phase not as big a concern, but if you are getting 120V single phase from a 240 single phase system then it is.

If you are feeding from a single 50A connection using the Y connector then you wouldn't have to worry about the cross-connection because you will always be on the same phase. If that is the only way you will feed both Connection 1 and Connection 2 at the same then you could wire the input to Heat Pump 1 to a breaker on Connection 1 and leave it connected to the breaker on Connection 2 at the same time, and if you end up with both breakers closed it would not be a big deal, but only if you are sure you are feeding from the same source.

So, best not to bridge the two connections. So, install a DPDT switch between the existing CB on Connection 2 and Heat Pump 1. Wire one input to the existing CB, the other to Connection 1, and the output to Heat Pump 1. Then you can feed the heat pump from either source, without risking a C1 to C2 connection that could short the phases of the marina system together.

[twistedtree]

Originally Posted by prroots

Thanks. I didn't make myself clear. I still want the option of feeding both heat pumps off connection 2 since if 50A is available I have a Y connector that feeds both inputs simultaneously.

Also, seems I might need a double pole, double throw switch so that the heat pump can be connected to circuit 1 or 2, but never both simultaneously. I'm thinking that there could be a serious problem if the heat pump is simultaneously fed by both inputs
Pete

Yes, that's what you need. The switch should be mechanically interlocked somehow so you are not inadvertently connecting the two 30A circuits together.

[btrayfors]

Two cautions:

1. 30A circuits in marinas really aren't capable of carrying 30A continuous. This is for several reasons, including lousy 30A connectors (the design stinks), surface corrosion on the contacts, "copper creep" within the connectors, etc. You can really only count on about 24-25A continuous.

2. Beware of 50A to two 30A "splitters". Problem is, you could draw as much as 50A thru EACH 30A connector, since the 208V circuit is protected by 50A breakers. That, of course, would be a very bad thing to do.

DSanduril had some very good advice above.

FWIW,

Bill

[prroots]

Thanks for the great feedback
Pete

[prroots]

As suggested on another thread, why not use a Y adapter that splits one 30A circuit into two 30A circuits. Obviously one has the same problem of potentially overloading the circuit, but otherwise it would seem to work electrically. Don't know if they make this adapter, but surely one could be made

Edit: this seems to be the right product:
http://www.marinco.com/product/y-ada...30-amp-locking
Pete

[Dsanduril]

Well now, there's a simple solution that was too much of not seeing the forest for the trees. Only problem with it is trying to draw more than 30A because you have both connections plugged in, and we're already in that boat. I like it. Lots simpler. Unless you really want to make is so that Heat Pump 2 can't be turned on no matter what.

[Adamante]

I am shooting from the hip here, but if it were my boat, I wouldn't use a DPDT switch - unless it would be guaranteed to always break-before-make and to never fail (probably expensive). If the contacts should ever hang up, or otherwise fail, there is the potential for a very interesting phase-to-phase short on a relatively flammable boat.

Instead, I would install a regular domestic duplex outlet rated for 30 amps and wire one of the outlets to Connection 1 and the other outlet to Connection 2. I would attach a male plug on the the Pump 1 feed wire.

All the switching would then be done manually by removing the plug from one the outlets and plugging it into the other outlet, based on the configuration of the shore service.

All this could be done with about 15 bucks worth of parts from Home Depot: one male AC plug rated for 30 amps, one duplex outlet rated for 30 amps, a junction box, a cover plate, and maybe some extra wire.

I admit it's not nearly as elegant as a DPDT switch, but it's totally fool-proof . No chance of creating a phase-to-phase short.

But again, I would do this only if it were my boat...

[Dsanduril]

As a proponent of the KISS principle for cruising I can't believe I missed the obvious as Pete suggested from the other forum. Gets rid of all new wiring on the boat. If you already have the 50A cable with the Y connector on the end, how about:

Pigtail Adapter, 30 Amp Locking To 50 Amp Locking | Marinco

That way you have fewer things to carry on the boat. When a 50A receptacle is available just plug in. When a single 30A is available plug in using the adapter and the 50A cable. Gives you the added advantage of using a larger conductor when you are running close to full load. Have to be careful about what you turn on, but that's going to be the case regardless of what solution you use when you only have one 30A circuit.

And, if you really want, you can carry two 30A cables for those occasions when two separate circuits are available.

[prroots]

Originally Posted by Dsanduril

As a proponent of the KISS principle for cruising I can't believe I missed the obvious as Pete suggested from the other forum. Gets rid of all new wiring on the boat. If you already have the 50A cable with the Y connector on the end, how about:

Pigtail Adapter, 30 Amp Locking To 50 Amp Locking | Marinco

That way you have fewer things to carry on the boat. When a 50A receptacle is available just plug in. When a single 30A is available plug in using the adapter and the 50A cable. Gives you the added advantage of using a larger conductor when you are running close to full load. Have to be careful about what you turn on, but that's going to be the case regardless of what solution you use when you only have one 30A circuit.

And, if you really want, you can carry two 30A cables for those occasions when two separate circuits are available.

Yes, I'm also a proponent of the KISS principle and I missed it as well. We are used to watching our current draw with simple rules so I'm not too worried about that. Thanks for the additional idea. My plan is to search for the Y adapter at marine surplus stores since I don't feature paying new prices.
Pete

[prroots]

Originally Posted by Adamante

I am shooting from the hip here, but if it were my boat, I wouldn't use a DPDT switch - unless it would be guaranteed to always break-before-make and to never fail (probably expensive). If the contacts should ever hang up, or otherwise fail, there is the potential for a very interesting phase-to-phase short on a relatively flammable boat.

Instead, I would install a regular domestic duplex outlet rated for 30 amps and wire one of the outlets to Connection 1 and the other outlet to Connection 2. I would attach a male plug on the the Pump 1 feed wire.

All the switching would then be done manually by removing the plug from one the outlets and plugging it into the other outlet, based on the configuration of the shore service.

All this could be done with about 15 bucks worth of parts from Home Depot: one male AC plug rated for 30 amps, one duplex outlet rated for 30 amps, a junction box, a cover plate, and maybe some extra wire.

I admit it's not nearly as elegant as a DPDT switch, but it's totally fool-proof . No chance of creating a phase-to-phase short.

But again, I would do this only if it were my boat...

Good point; a failure of the DPDT switch could cause a problem. Actually, I'm leaning strongly towards the Y adapter idea which avoids any new wiring, is simple, and doesn't risk the potential of phas to phase shorts.
Pete

[GordMay]

Marinco #157AY - Y Adapter, 2-30 Amp Locking To 30 Amp Locking
Male Connector: 30A 125V Locking, attaches to dockside receptacle or cordset
Female Connector: 2-30A 125V Locking w/ Sealing Collar System, attaches to cordset or boat inlet
$ 199.95 / Each ➥ Marinco 157AY Y Adapter 2-30A to 1-30A - Shorepower Y-Adapters by Discount Marine Supplies

See Marinco ➥ Shore Power Adapters | Marinco

And Charles ➥ Marine: Cable Adapters & Smart Y Adapters

[Adamante]

Originally Posted by prroots

Good point; a failure of the DPDT switch could cause a problem. Actually, I'm leaning strongly towards the Y adapter idea which avoids any new wiring, is simple, and doesn't risk the potential of phas to phase shorts.

Yes, that would be simpler. The only flaw I see is the risk of an overload if the other pump is inadvertently turned on. The shore service breaker would catch it, but I would be leery of deliberately creating a situation where I would be relying on a breaker trip.