Dubious Electrical Idea

[Lin]

I am thinking of reworking some of my wiring by removing the breaker box and replacing it with two smaller ones.  One would be just those circuits serviced by the inverter.  One problem I have is space for the panels.  I was thinking of saving space by using a smaller panel and double tapping some breakers.  My thought was that I could put one AC and one electric heater on the same breaker.  Although the total load would be greater than the 20 amp breaker rating, I do not see any situation where I would be using both heat and AC at the same time.  Does that make sense?

[Lee Bradley]

If you lose the wiring (short)  on one circuit, you lose both circuits. What brand breakers are you using?

[richard5933]

Depending on what type of breakers you're using, perhaps you can get tandems - two breakers that fit into one slot. I know that Square D makes them for the QO load centers.

The idea of running both the AC and electric heat on the same breaker might sound good now, but down the road it could lead to unintended results. My vote is to keep things up to code as much as is possible. I'd avoid the double tapping.

Alternatively, could you add a sub-panel that you could use to mount the additional breakers you really need?

Or, have you explored using a marine panel? There are some very compact panels for 120v systems that are used in marine applications that might suit your needs and allow you to install the correct number of breakers. There are also some marine panels that are actually two smaller panels combined into one housing, with the end result being like you describe with the inverter powering one half and the shore/gen power on the other half.

[Gary Hatt - Publisher BCM]

I see  no problems running the A/C and heat off one breaker as long as you don't turn them both on at the same time.  Worst case, you pop a breaker.  I was an electrician in a previous life and personally I like a lot of breakers as others have noted.  I would try to make room for a bigger panel at all costs and run as many circuits as possible because once you get things closed in, it is 10x harder to run more wires.

Two panels is fine too. I have two 120V panels in my bus. One for the inverter circuits and one for Shore/Generator circuits i.e. A/C, heat, Microwave.  As for double-breakers, I have used those but only when necessary.  Wiring gets a bit tighter when you try doubling breakers, but that would be a viable solution to run the A/C off one and heat off the other side.   You also need to keep in mind when you are hooked up to 50A, you are running two separate legs and they should be balanced throughout your panel but that is an entirely different subject. 

Check out The Bus Converters Bible here.  If you are not a subscriber now, it is worth becoming a subscriber just to be able to have access to this Book on PDF.  We will be posting all Books on PDF over the next couple of months.  https://www.busconversionmagazine.com/books-on-pdf/

Gary

[Lin]

The simple act of double tapping is not much of a concern since one can get breakers that are design for it or just use a wire nut to combine two wires to one that would go to the breaker.  The original owners ran his wiring for convenience so that lights on one side of the coach are on a separate circuit than lights on the other side.  In other words, there might be just four LED bulbs on one circuit.  So combining those circuits seems to be of no consequence.  It is in combining a heat circuit with an AC circuit, knowing that the breaker could not really service both, that I am toying with.  But I just don't see why I would consciously turn on both heat and AC at the same time (if I did, I probably should not be driving a bus anymore).

Richard: I do not know anything about marine panels, so I should research that.

Gary:  Actually, I only have one leg of 50 amps that serves both bars in the panel.  I do not have any 220v loads, so this has worked fine allowing me to have a three wire shore cord that is 25% lighter. I probably should try to figure out a way to squeeze bigger panels in.  My current single panel is about 10x12.  For two 4space/8circuit panels it looks like I need a good 14x14, so something else might have to be moved.  I do intend to use double breakers also.

[richard5933]

How did you end up with one leg of 50 amps? That's a rather unique situation.

Here's just one example of a marine panel so you can see some of the options. They are not the cheapest, but they do pack a lot into a small space.

https://www.go2marine.com/product/162182F/ac-12-position-breaker-panel-5301-paneltronics.html

Lots of other options out there. We've got a similar panel on our Custom Coach conversion, and the fact that it takes up so little space as compared to a household style box is why we haven't changed to something else yet.

[Melbo]

Here in New Mexico evaporative cooling is very common and one breaker serves both the furnace and the cooler.  The difference that I would see is that here when the cooler is in service the furnace is unplugged or if the furnace is in service the cooler is unplugged.  They share the same duct system so only one appliance is used at a time.  Kind of like some people do not use transfer switches they physically move a plug to switch between generator and shore power.

Good luck with your planning.  A schematic is probably the best place to start and work from there.  

GE used to make a very compact panel.  I have installed them on older homes where there was not much room for a new panel.  Something like an 8 inch by 12 inch with like 8 circuits.

GE Energy Industrial Solutions TL412CP Main Lug Indoor Load Center, 125-Amp


HTH

Melbo

[oltrunt]

Once I overcame the "Green Acres effect" by actually testing loads to determine the best way to wire things, I've been quite happy with the results of over loading my breakers.  But then my 120v system is only 30 amps with 2, 15 amp slow blow breakers.  Jack

[bigred]

FWIW,You could be safe as well as in line with the code ,from your breaker feed a double throw switch then feed your ac and heat off the switch .This way it is impossible to have them both on at the same time.

[eagle19952]

my coach is exactly that way and has been for ever. (I've owned it since 02-03) but, i have tandem breakers on 110v (ok 120v ).
my heat AC <are 220v> and hot water <110v> are not on the inverter.
everything else is. obviously, the inverter/charger is on the main too.
and i have a piece of 6/4 that i can jumper the sub if i had to have work done on the inverter...i tape back the red wire...or was it the black ?
but, now i carry a spare inverter too.
because I might be a hoarder
the inverter fed sub-panel has been in service 24/7 for 16 years, except for short periods of down time...
inverters need tlc too.

[TomC]

I have three circuit breaker boxes. One for shore (one leg of 50amp) or generator (two legs of 50amp wired straight 120vac). Then main circuit breaker box with one 30amp circuit feeding through inverter to my inverter circuit breaker box. All Murray from Home Depot. Simple, easy to service, but everything is manually operated. Good Luck, TomC

[Melbo]

I like the idea of the three way switch.  Be sure that it is rated for the amperage that you would run through it.  It would keep you from having both appliances on at the same time and would save you a breaker space in the panel.  You would know when you are going to need heat or cool and just flip the switch from one setting to the other.

Melbo

[Lin]

Richard: When I did the electrical on my last bus, I chose to make it with just one 50 amp leg. I put a jumper wire in the panel to reach the other bar. I worked fine since I do not have 240v loads.  I thought at the time that it was probably unique.  However, when I bought this bus it had a similar setup.  This makes it either a very large coincidence or that there are a lot more out there who used similar logic. As mentioned, the shore cord is 25% light and therefore easier to handle and store.  The marine panel looks interesting but I would probably go with a more budget solution.

Eagle: Thanks for the reminder to have some bypass system in case the inverter fails.  On my present system I manually move the plug from shore to generator.  The transfer switch switches from shore/generator to inverter.  Even that has a bypass system though.  Since the transfer switch probably should be replaced, I thought that this might be the time to change the system a bit.  Although it generally works fine, there have been times when I forgot to turn off the water heater when the system switched automatically to inverter. In that case, it does not destroy the batteries but does let them run down to around 10v for the inverter to close down.

Now, I wanted to throw out a hypothetical idea.  Suppose instead of using two small boxes, I just use the box I have now changing it around a little.  What if I put all the non-inverter loads on one bar with one more circuit for the inverter?  The inverter could than feed the other bar where all the low amperage circuits would be.  Is there something inherently evil about that? In my case there could be a problem due to the generator, which actually does supply 2 50 amp legs to the panel. Of course that could be modified but I am not sure that is alright to do.

[richard5933]

Richard: When I did the electrical on my last bus, I chose to make it with just one 50 amp leg. I put a jumper wire in the panel to reach the other bar. I worked fine since I do not have 240v loads.  I thought at the time that it was probably unique.  However, when I bought this bus it had a similar setup.  This makes it either a very large coincidence or that there are a lot more out there who used similar logic. As mentioned, the shore cord is 25% light and therefore easier to handle and store.  The marine panel looks interesting but I would probably...

I think I understand, but how do you plug in when you're not at home? Or do you?

Our current bus, as well as our old bus, were both built by Custom Coach. They also used a non-standard method by running two 30-amp hot leads instead of two 50-amp. Not sure why, but it took a while to figure out on our first one since someone had installed the wrong receptacle for the shore cord.

Whatever you do, my suggestion would be to be sure to label everything and make sure that someone can't accidentally plug it into the wrong type/style of power source.

[Lin]

It works with a standard 50 amp rv receptacle.  The plug is wired to only three blades (hot, neutral, ground).  I actually have removed the fourth blade from the plug since it serves no purpose.  I only have a 30 amp connection at home, so we use a common adapter pigtail.