Using branch connectors to wire a charge controller

johnnysolar

I'm thinking about wiring a midnite classic 150 to a 3kw (12 Suniva 245's) (Ive done my voltage calcs so I wont be in hyperVOC) array in the following way:
4 strings of three in series. I was planning on using 2 sets of branch connectors on the roof so I only have to pull 5 wires instead of 9 down through the roof and landing in the combiner, on two 30amp dc breakers. Anyone see anything wrong with this. Anyone using branch connectors for wiring charge controllers. House roof is super steep metal, 12/12. Branch connectors are like a ready made solar wiring harness. For example, it would be 2 male MC4 connectors that y into a single wire with an mc4 on that end. I hate the idea of putting the combiner on the super steep inaccessible roof.

Cariboocoot

Re: Using branch connectors to wire a charge controller

Well this is not recommended.

The four parallel connections should have over-current protection on each one. This is usually done in the combiner box, which is usually located with the array. That's why combiner boxes are weather-tight. As for putting it on a steep roof, you usually don't have to access the box after the install. A disconnect near the controller can be used to shut off the array if needed.

If you do it the way you describe and you get a panel short the other panels can feed it short-circuit current until something ignites. I doubt such an install would pass inspection.

johnnysolar

Re: Using branch connectors to wire a charge controller

I just hate the idea of hiding a combiner box full of breakers in it that could trip and need to be reset up on a 12/12 roof. In the past, I have put them in the attic directly underneath the array or in the mech room if it is close enough. I am going to keep doing this unless someone has a really good idea why I shouldn't.

Cariboocoot

Re: Using branch connectors to wire a charge controller

johnnysolar wrote: »

I just hate the idea of hiding a combiner box full of breakers in it that could trip and need to be reset up on a 12/12 roof. In the past, I have put them in the attic directly underneath the array or in the mech room if it is close enough. I am going to keep doing this unless someone has a really good idea why I shouldn't.

Thought I just said why it shouldn't be done.
Anyway, the only reason the breaker should trip is if a panel shorts. Sometimes it might trip for a defective breaker. Either case is highly unlikely and would indicate a need for service anyway.

bill von novak

Re: Using branch connectors to wire a charge controller

johnnysolar wrote: »

I just hate the idea of hiding a combiner box full of breakers in it that could trip and need to be reset up on a 12/12 roof.

Well, if they trip, you are going to have to go up on the roof anyway to fix the problem that caused them to trip. These won't trip from too much demand on the system; they will only trip when something is broken (and in some cases about to start a fire.)

Dave Angelini

Re: Using branch connectors to wire a charge controller

bill von novak wrote: »

Well, if they trip, you are going to have to go up on the roof anyway to fix the problem that caused them to trip. These won't trip from too much demand on the system; they will only trip when something is broken (and in some cases about to start a fire.)

A defective breaker can trip and it is a nuisance! You have to have them though and it is another reason that solar on a roof is a pain!

Cariboocoot

Re: Using branch connectors to wire a charge controller

Dave Angelini wrote: »

A defective breaker can trip and it is a nuisance! You have to have them though and it is another reason that solar on a roof is a pain!

One of the reasons I tend to prefer fuses at that point. They rarely 'nuisance pop'.
And sometimes the roof is the only place you can put the panels.

solar_dave

Re: Using branch connectors to wire a charge controller

One way to put the combiner in the attic is to install a weather head to run the strings into the attic. This is how they did my 8 strings of 9 panels. It is strapped in 2 places in the attic along side a truss and flashed on the roof.

BTW they combined to 2 output lines for the dual inverters.

vtmaps

Re: Using branch connectors to wire a charge controller

bill von novak wrote: »

Well, if they trip, you are going to have to go up on the roof anyway to fix the problem that caused them to trip. These won't trip from too much demand on the system; they will only trip when something is broken (and in some cases about to start a fire.)

I am in complete agreement. Another good reason to have the combiner outside the house is for lightning protection. If you can divert the lightning (with a lightning arrestor at the combiner) before it enters the house, so much the better.

--vtMaps

johnnysolar

Re: Using branch connectors to wire a charge controller

Just to be totally clear. You are all saying that I should mount the combiner on the roof with the array and not inside the attic underneath it. I understand the I should have overcurrent protection on every string and I usually put a midnite SPD in the the combiner anyway. Anyone have a picture of the way they have done this on a flush mount.

vtmaps

Re: Using branch connectors to wire a charge controller

johnnysolar wrote: »

Just to be totally clear. You are all saying that I should mount the combiner on the roof with the array and not inside the attic underneath it. I understand the I should have overcurrent protection on every string and I usually put a midnite SPD in the the combiner anyway.

One more detail... from the combiner on the roof, you want the ground wire to run outside the house to the ground rod... don't bring lightning into your house.

--vtMaps