what amp breaker to use

Stu Piddly

I have purchased 4 kyocera 135 panels and a TriStar 45 PWM controller,I have a bunch of square D QO boxes and various sizes of breakers,15,20,single and tandem,30,40double pole. I have read all the info a search on this site turned up using the QO stuff. If I read it right, it would be ok to use QO breakers in a 12 or 24 volt system,for now I am going 12volt. I am going to run 4 panels in parallel,I was going to run the panel cables into a small QO box(QO200TR)which has space for two breakers. I will use two 2 pole tandem breakers so each panel will have its own breaker/switch. These breakers use a single space,but have two separate buttons/circuits. I have these tandem breakers in 15 and 20 amp,which one would be better to use? 15 or 20 amp,This will be my combiner box and disconnect between my array and ts-45

niel

Re: what amp breaker to use

you can go by the series fuse rating and that pv shows 15a so that's what you want to use.

Cariboocoot

Re: what amp breaker to use

The K135's have and Isc of 8.37. Usually no more than a 10 Amp fuse is required. Using 20 Amp or even 15 Amp breaker per panel is larger than necessary and not in accordance with NEC rules.

Make it easy on yourself: use four 10 Amp automotive fuses before combining the panel outputs and put the lot on a 40 Amp disconnect near the controller.

Watch out for Voltage drop: your running fairly low Voltage (12 Volt nominal) at fairly high Amperage (about 30) which can be problematic with wire size/length. For even ten feet of run you'd need 6 AWG wire to handle the combined current with less than 3% Voltage drop, and V-drop is savage on 12 Volt systems.

Consider getting an MPPT controller if you haven't bought the PWM yet, or going to a 24 Volt system. That way you could up the array Voltage and reduce the current and utilize smaller wire/longer runs.

Stu Piddly

Re: what amp breaker to use

can the larger QO breakers be used for a battery disconnect/breaker? I will be using two 6volt golf cart bats in series. I may get a morningstar suresine inverter,could or should I use a QO breaker as a disconnect there?

niel

Re: what amp breaker to use

qo breakers are fine to use at 12v and 24v dc and the series fuse rating of a pv is based on nec type requirements so that is fine to use that 15a breaker for each pv. there isn't any reason why going to 10a would hurt either, but you don't have 10a breakers on hand.

the higher rated qo breakers can be used on the input of the controller and batteries too.

Stu Piddly

Re: what amp breaker to use

Cariboocoot wrote: »

The K135's have and Isc of 8.37. Usually no more than a 10 Amp fuse is required. Using 20 Amp or even 15 Amp breaker per panel is larger than necessary and not in accordance with NEC rules.

Make it easy on yourself: use four 10 Amp automotive fuses before combining the panel outputs and put the lot on a 40 Amp disconnect near the controller.

Watch out for Voltage drop: your running fairly low Voltage (12 Volt nominal) at fairly high Amperage (about 30) which can be problematic with wire size/length. For even ten feet of run you'd need 6 AWG wire to handle the combined current with less than 3% Voltage drop, and V-drop is savage on 12 Volt systems.

Consider getting an MPPT controller if you haven't bought the PWM yet, or going to a 24 Volt system. That way you could up the array Voltage and reduce the current and utilize smaller wire/longer runs.

concerning the voltage drop,my combiner box will be about 5 feet from my controller,the boxes will accept 2 AWG so I thought that is what I will use,contoller to batterys will be about 2 feet. I see that I can only buy MC4 cables in 10 AWG,how far can my panels be from my combiner using #10 cable and be under 3% drop

Cariboocoot

Re: what amp breaker to use

Stu Piddly wrote: »

concerning the voltage drop,my combiner box will be about 5 feet from my controller,the boxes will accept 2 AWG so I thought that is what I will use,contoller to batterys will be about 2 feet. I see that I can only buy MC4 cables in 10 AWG,how far can my panels be from my combiner using #10 cable and be under 3% drop

Looks like no more than 20 feet by my calculator.

2 AWG is pretty big. If you don't have it on hand, consider going a bit smaller as you could still stretch out the distance some and maybe save a little money.

Cheap, aren't I?

Stu Piddly

Re: what amp breaker to use

I have about 100 feet of mobile home umbilical cord on hand,it has three #6 and one #8 conducter wrapped in black rubber,very flexible,it is huge and heavy,I could strip the outer coating off and separate,cheap is my middle name,but people call me Frugal Dude

Vic

Re: what amp breaker to use

Stu,

I believe that the DC rating of the QO breakers applies ONLY to the Square D QO and QOB breakers, as singles and duals, but NOT Tandem breakers. The Tandems are QOT.

The current range that the DC rating applies to seems to be in the range of 10-70 Amps, but the 10 breakers seem to be specifically excluded from the DC rating. And the DC rating applies up to 48 Volts nominal.

The DC rating is probably not listed on the breaker's tag, so it is possible in a system that will be inspected that this breaker series may not fly.
YMMV, Vic

Stu Piddly

Re: what amp breaker to use

Vic wrote: »

Stu,

I believe that the DC rating of the QO breakers applies ONLY to the Square D QO and QOB breakers, as singles and duals, but NOT Tandem breakers. The Tandems are QOT.

The current range that the DC rating applies to seems to be in the range of 10-70 Amps, but the 10 breakers seem to be specifically excluded from the DC rating. And the DC rating applies up to 48 Volts nominal.

The DC rating is probably not listed on the breaker's tag, so it is possible in a system that will be inspected that this breaker series may not fly.
YMMV, Vic

I have been reading the data sheets from square D for a couple of days,the way I read it 15 amp QOT is in the QO line and is between 10 and 70 and was not excluded in the footnotes,you have a point though,maybe a call to square D is in order to clarify

Cariboocoot

Re: what amp breaker to use

Many is the time when an inspector has looked at a part and not seen the DC rating stamped on it and said "no". :cool:

Stu Piddly

Re: what amp breaker to use

this system will be installed in a cargo trailer,there wont be any inspection,however,I still want to use the correct breakers for the application,if QOT are DC rated and correct for the application,then I will use them,the tough part will be finding the correct person at square D to ask

Vic

Re: what amp breaker to use

Stu,

Just went back to review the QO-line specs. I dunno if the QOTis DC rated. In the photo of the various styles of QOs, there is a single pole, double, and three pole shown, but NO tandem.

I do not know. As you know, there is a limit on the number of Tandems that one can mount in one load center. Am sure that you have checked to make certain that the Tandems that you need to mount in the candidate box will all fit.

Good Luck, hope you find someone to communicate with @ Schneider/SQ D. They are a huge company -- about 40 Billion Euros in sales last year. Vic

Stu Piddly

Re: what amp breaker to use

Vic wrote: »

Stu,

Just went back to review the QO-line specs. I dunno if the QOTis DC rated. In the photo of the various styles of QOs, there is a single pole, double, and three pole shown, but NO tandem.

I do not know. As you know, there is a limit on the number of Tandems that one can mount in one load center. Am sure that you have checked to make certain that the Tandems that you need to mount in the candidate box will all fit.

Good Luck, hope you find someone to communicate with @ Schneider/SQ D. They are a huge company -- about 40 Billion Euros in sales last year. Vic

the photo I looked at,the single pole IS a tandem.next to a double and a triple,look close and you will see two narrow buttons,general information,page 3,also check out square D data bulletin 0601DB0401 all about DC apps, but over my head,I have a bunch of the QO singles,I guess I can just use four singles instead of two tandems,as I know that will work

Vic

Re: what amp breaker to use

Stu,

Yes, you are correct, the one on the left does have two handlettes, altho, it is referred to as a one pole breaker.

I dunno. I did look at the bulletin, and it was not very informative IMHO.

Anyway, you seem to be researching this well, Good Luck, Vic

Stu Piddly

Re: what amp breaker to use

I went to schneider electric website>support>FAQ >lots of good stuff there,ask and you get answers, now. Every question you can think of has been asked,the tandem breakers cannot be used,long list of boxes and breakers can be used,if you need parts with DC rating tags on them it gives part # and how to order them. It is the best FAQ I have ever seen and used!!!!