Is There a Generator Load Shedding Panel That Is Not Also a Transfer Switch?

[Tom Jones]

Hi all, thanks for the forum. I have been coming here for many years but never had occasion to post. It seems that whenever I have a question, a Google search always turns up the answer somewhere in this forum where it has already been solved for me so I never needed to sign up. On to my question: A couple of years ago I installed a GE "Symphony" small standby genset (really Briggs & Stratton) and transfer panel that were a "matched set" if you will. The transfer panel is simply a main and a generator breaker along with the usual circuitry, but additionally it has two current transformers that go over the generator power leads and it will open certain contacts in the panel if the generator load exceeds a certain level. I thought this was a great new feature. Fast forward to today, I am looking at a different installation that has a main panel, manual transfer switch, and subpanel already installed, and in the interest of saving cost, I would like to not have to replace the entire transfer switch. I was hoping somebody makes a box that can simply shed loads from the generator; in this case it would be the HWH, heat pump, and maybe one or two others, and reconnect them when the additional load is reduced automatically like the GE/B&S unit above does. Does anybody make such an animal? If not, would you have any recommendations about a transfer switch that includes it, with the understanding that the generator is going to be manually started, so that the transfer switch can get along with that as well? (i.e. doesn't rely on the generator starting immediately in case of main power loss)

 

[augie47]

Possibly:

http://w3.usa.siemens.com/us/intern...s/Power Master Data Sheet RPFL-POWMA-0307.pdf

 

[gar]

130317-0825 EDT

The following is not a direct answer for your question.

In my opinion there are numerous questions to ask in sizing a residential backup generator. Some are:

1. What is the purpose?

Emergency conditions that rarely occur, or once a month for many days? North or south location? Any special equipment loads?

In my case I have two freezers, one refrigerator, and one furnace blower motor that must be backed up. Beyond that possibly 1 kW is enough. Roughly speaking under worst case conditions I need 2.6 kW of steady state power. To this has to be added some capacity for motor inrush. Thus, I power the whole house with a 5 kW, and don't power things that are not really needed.

I am advising a neighbor and it looks like 7.5 kW is more than adequate for them. They have a moderate size three phase air conditioner (the only three phase load), and a smaller single phase unit. These will not be powered under emergency conditions.

It is important to try to ask the correct questions.

I should point out we are in a natural gas area, and hot water, and cooking are usually gas supplied (1/3 the cost for energy).


2. Shedding load.

If there are loads that need to be automatically dropped when primary power is lost, then you could use a holding contact type of contactor circuit to drop the loads on loss of primary power, or a mechanically latched relay that is triggered off on loss of primary power.

If you are in an all electric area and need electric hot water, and electric heat, then it is a more complex problem. I doubt there are many areas where air cooling in a residential application is an absolute necessity. Man has lived a very long time without air conditioning, even in places like Cuba or Panama (gets quite humid there).

The GE system you mentioned has interesting possibilities, but what does it do when first transferring to generator and many motors simultaneously try to start? Are the different loads sequenced on start up? Also does it make judgements on whether a load can be added?

From discussions with my neighbor you really want to power the whole house, but just turn off unnecessary loads.

.