GFI wiring

Joe94

I got a response from the folks at Morningstar about my suresine not switching to standby. They told to make sure that the AC nutral is tied to the DC earth ground. if I recall correctly I read somewhere in my midnight classic manual that it is important not to connect the earth ground to the negative for the ground fault protection to work correctly. Will connecting the AC nutral to the DC ground prevent the ground fault on the controler from functioning correctly?

vtmaps

Re: GFI wiring

Joe94 wrote: »

I got a response from the folks at Morningstar about my suresine not switching to standby. They told to make sure that the AC nutral is tied to the DC earth ground. if I recall correctly I read somewhere in my midnight classic manual that it is important not to connect the earth ground to the negative for the ground fault protection to work correctly. Will connecting the AC nutral to the DC ground prevent the ground fault on the controler from functioning correctly?

In general, it is very important for your DC negative to be grounded. For small systems (especially 12 volt) its not as important. It is required by code for a permanently installed system in a dwelling. When the DC negative is NOT connected to ground, the system is said to be floating and it is required to have circuit breakers or fuses in BOTH positive and negative wiring.

NEC requires DC GFP on roof-mounted arrays. A DC GFP is a small circuit breaker (1 amp or less) that is the bond between DC negative and ground. The circuit breaker is physically ganged to a larger breaker that can disconnect the battery or the solar panels from the system. If there is a fault that results in current flowing through the little GFP breaker, it trips and opens the larger breaker. The problem with the DC GFP is that when it trips it breaks the bond between DC negative and ground. That means the system is floating, but doesn't have fuses in the negative wiring. This is dangerous and, in fact has caused or exacerbated fires.

If you create another bond between DC negative and ground, you will have "shorted" the small GFP breaker and it will never trip. Many of the smartest folks around have done that, but they won't advise you to do it yourself if it violates code.

--vtMaps

Cariboocoot

Re: GFI wiring

Joe94 wrote: »

I got a response from the folks at Morningstar about my suresine not switching to standby. They told to make sure that the AC nutral is tied to the DC earth ground. if I recall correctly I read somewhere in my midnight classic manual that it is important not to connect the earth ground to the negative for the ground fault protection to work correctly. Will connecting the AC nutral to the DC ground prevent the ground fault on the controler from functioning correctly?

Morningstar should have said to be sure one of the AC outputs is tied to Earth ground. These gives it zero Voltage potential in respect to ground and makes it the neutral line. It is not necessary to have it connected to DC (-), although if that is grounded it is recommended that the same ground be used for both.