Author Topic: Breaker/wire sizing advice on Classic 150  (Read 461 times)

SolarMusher

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Breaker/wire sizing advice on Classic 150
« on: July 18, 2021, 10:37:41 AM »
Hi All,
I have to rewire a poorly designed 48Vdc system with a 4725 watt array (21 x 225 watt old poly).
According to the classic tool, a single Classic 150 would be ok. Max output would be 80A at 58.8Vabs.
I'm wondering if this 80A output on a small #4 wire with a 100A MNEDC breaker (according to the Midnite breaker sizing chart) would be safe enough?
Any feedback appreciated.
Thanks,
Erik
Off Grid with 4kw PV | 2x Classic 200/WBjr | 2x Outback VFX3648 Epanel | 3x SPD300 + 1x Schneider HEPD80 | Hub + Mate + PSX-240 | Volthium 400Ah/51.2V LFP battery bank + Trimetric | 1500 watts AC water heater | Kubota 11kw GL diesel generator

boB

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Re: Breaker/wire sizing advice on Classic 150
« Reply #1 on: July 18, 2021, 12:53:56 PM »

Actually, for NEC,  less than 100A I think #6 is OK...   #4 is better of course but it's a short run so not much launch.

Problem is with stranded #4 you might have  hard time getting it to fit.  Solid #4 fits pretty well though.

You can always clip off strands of #4 until it fits which would still be better than #6.

boB
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Vic

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Re: Breaker/wire sizing advice on Classic 150
« Reply #2 on: July 18, 2021, 02:01:26 PM »
Regarding #4 AWG cable fitting into the Classsic terminal block,  it fits fine,  when using 19 strand (and quite possible 31 strand) THHN type of cable.

Think that in Canada,   compact conductor Building wire,  is often not referred to as,  THHN,  but there is something very similar.

And,  of course,  fine-stranded cable should not be used (directly)  in most screw-terminal connectors (IMO).

Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

SolarMusher

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Re: Breaker/wire sizing advice on Classic 150
« Reply #3 on: July 18, 2021, 04:28:02 PM »
Hi Bob and Vic,
Hope you are going fine!
It's a bit complicated to find the right stranded THHN wire here in Canada to get the job, so I'm using #4 19 strands building wire and it fits fine in Epanel/Classic busbars.
My question was more related to the max ampacity of a #4 cooper wire at 75°C (85A from chart). Usually, I mount a 80A breaker for #4AWG, so just wondering how a 100 amps MNEDC breaker could be effective to protect a #4AWG wire (building wire)?
Thanks,
Erik
Off Grid with 4kw PV | 2x Classic 200/WBjr | 2x Outback VFX3648 Epanel | 3x SPD300 + 1x Schneider HEPD80 | Hub + Mate + PSX-240 | Volthium 400Ah/51.2V LFP battery bank + Trimetric | 1500 watts AC water heater | Kubota 11kw GL diesel generator

Vic

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Re: Breaker/wire sizing advice on Classic 150
« Reply #4 on: July 18, 2021, 05:04:38 PM »
Hi Erik,

What is the length of the #4 cable,  and,  it is it in conduit?
How many current-carrying conductors are being run together with this #4 cable?  Is the ambient temperature elevated,  at times?

NEC is very conservative on Ampacities,  and most other things.   If this installation is being inspected,  an inspector may flag it.

If this cable is short,   and in free air,  you are probably good.

As you well know,  sometimes one can run a short #4 cable,  to the DC breaker,  and make the transition to a larger cable at the other side of this breaker.   This might require adding a breaker box,  etc  ...

I am NOT a Code Expert.   FWIW,   Good Luck,   Erik,  nice to see you here.  Take care,  Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

SolarMusher

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Re: Breaker/wire sizing advice on Classic 150
« Reply #5 on: July 18, 2021, 08:29:27 PM »
Vic,
I'm talking about the inside wiring of a MN-Epanel, from classic bat to the lower part of the 175A battery disconnect (including the CC breaker wiring). Maybe 4 feet long max up to the 2/0 inverter cable.
No conduit, as we are talking about the inside of Epanel installed in the basement at room temp (15/20°C).
Vic, in fact my question is mostly related to a 100 amps breaker (MNEDC-100) versus a #4AWG wire rated at 85A max at 75°C.
Are you more busy this year than the last one with covid in California?
Erik
Off Grid with 4kw PV | 2x Classic 200/WBjr | 2x Outback VFX3648 Epanel | 3x SPD300 + 1x Schneider HEPD80 | Hub + Mate + PSX-240 | Volthium 400Ah/51.2V LFP battery bank + Trimetric | 1500 watts AC water heater | Kubota 11kw GL diesel generator

Vic

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Re: Breaker/wire sizing advice on Classic 150
« Reply #6 on: July 18, 2021, 09:41:05 PM »
Hi Erik,

To me,  that cable inside the e-panel  is "free air"  I would not worry about it at all (but that's just me).  It should be fine at 100 Amps continuous IMO.

Generally,  our economy came roaring back,  some months ago,   but as you know,  the Delta variant is surging in this state.   It looks like Canada is doing fairly well  --  fairly high vaccination rates,  and,  IIRC,   number of cases coming down.

How are things for you,  up there?

Take care,  Good Luck,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

SolarMusher

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Re: Breaker/wire sizing advice on Classic 150
« Reply #7 on: July 19, 2021, 06:42:58 AM »
Hi Vic,
Last year was a nightmare with a bunch of cancellations in May and I had to work until January in ten inches snow to get decent sales, really tough. 2021 is crazy, too much works and lacks of parts everywhere to get all the jobs done, a bit complicated.
Yes, our vaccination rate is better in Canada so fingers crossed for the delta variant on next fall.
Our Quebec prime minister said from the beginning : "it will be fine, it will be fine" just like a mantra, LOL!
Anyway, our lake is beautiful this morning!
keep strong!
Erik
« Last Edit: July 19, 2021, 06:53:48 AM by SolarMusher »
Off Grid with 4kw PV | 2x Classic 200/WBjr | 2x Outback VFX3648 Epanel | 3x SPD300 + 1x Schneider HEPD80 | Hub + Mate + PSX-240 | Volthium 400Ah/51.2V LFP battery bank + Trimetric | 1500 watts AC water heater | Kubota 11kw GL diesel generator

Vic

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Re: Breaker/wire sizing advice on Classic 150
« Reply #8 on: July 19, 2021, 12:34:40 PM »
Hi Erik,

WOW,  sounds like you had some difficult working conditions in the Winter.   Being in CA,  cannot even imagine what that must be like  ...   we are staying here!

Glad that your PM  awakened.

Good that you are busy,   but sounds like the supply-chain has not settled down yet.

Good Luck,  enjoy the Summer,  and hope that you will have a prosperous year,  and for years to come.

Thanks for the note,  be safe,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!