MidNite Classic 200 and wiring to NEC code help please.

[DavidH]

Hi all,

So I'm the owner of a MidNite Classic 200 and I'm building a smaller backup solar power system (1000WH). I invested in the Classic 200 to allow room for upgrading in the future and the system is 24V. I've purchased the Midnite Solar MNDC Series C Aluminum Enclosure to house the wiring, breakers etc.

So here's my struggle with NEC code compliance.

The MidNite classic 200 can accept a max size of 4 AWG wire for the DC output. To be code compliant it must be able to cope with the max 79A DC output at 125% = 98.75A.

Table 310.15(B)(16) Allowable ampacities of insulated copper conductors rated up to and including 2000 Volts, 60°C
through 90°C (140°F through 194°F), Not more than three current-carrying conductors in raceway,
cable, or earth (directly buried), based on ambient temperature of 30°C (86°F). Has the 4 AWG rated for only 95A at a 90C temperature rating of conductor.

The MidNite manual states the following:

The connector will take up to a #4 AWG. #4 AWG THHN when installed in the Classic and MidNite E-Panel is rated for over 100 amps and is therefore suitable for the highest power available from the Classic 150.

This obviously applies to the classic 200 since it outputs less amps than the classic 150. So this takes me to the conclusion that in the E-panel (which I believes includes the MNDC Series C Aluminum Enclosure I purchased) it is code compliant because it's based on the following:

Table 310.15(B)(17) Allowable ampacities of single insulated copper conductors rated up to and including 2000 Volts
in free air, based on ambient temperature of 30°C (86°F). This has the 4 AWG wire rated for 140A at a 90C temperature rating of conductor.

BUT and here's where I'm running into problems understanding - the same 4 AWG wire from the Series C enclosure should enter conduit leading to the battery compartment and conduit leading to the inverter if the system is inside a home. The conduit would only be a couple of feet of PVC piping (as everything is close together) but does that conduit then mean that to be code compliant I cannot use table Table 310.15(B)(17) to calculate a max ampacity of 140 for the 4 AWG wire (at 90C rated insulation) because it's not "free air" and would have to revert to Table 310.15(B)(16) which would require 3 AWG wire (which doesn't fit into the MidNite classic 200)?

Any help with this would be much appreciated!
Thanks

Here's the link to the two tables I'm referring to https://www.lapptannehill.com/pub/media/wysiwyg/pdf/AmpacityChart.pdf

[Vic]

Hi DavidH,

Agree,  that the e-panel and MNDC  enclosures  are more like free air than a raceway or conduit.

As an aside,   it is best to use the 75C rating for conductors that attach to breakers,   or similar devices.

What is often done,  is to use a conductor that is larger than #4 AWG THHN from the output of the battery breaker to the battery,  if that connection is not made inside the MN enclosure.

However,   I am NOT a Code Maven,   FWIW,   Vic

[DavidH]

Thanks Vic for the reply.

Yes, that makes sense - have the 4 AWG wire from the 79A classic DC output making a connection to the breaker and then on the other end of the breaker make the connection to the larger wire going into the conduit to the battery, so keeping to the code.

Ok, I took your advice to use the 75C rating and put together this pdf with the circuit diagram that comes with the MNDC enclosure. Does this look about right to you?

I'm considering whether to run the DC output from the classic down to the battery +ve terminal using AWG 3 or AWG 2 (if calculation in pdf is correct) instead of inside the enclosure at the breaker terminal - so that I can put a fuse on it (using the Blue Sea dual terminal fuse block).

[Vic]

Hi David,

If I understand,  correctly,  what you are thinking of doing  --  NO breaker on the Classic 200 output connection to the battery (?).

You WILL want a Disconnect on the Classic's battery connection.   This function is usually best done with a breaker.   The current rating of such a breaker probably could have a rating of 100 A.   There is a MidNite breaker in the MNEPV series,  (DIN Rail) that is rated at 100 A,   but it occupies two DIN spaces.   The other MNDC breaker series MNEDC also has a 100A breaker,   but may need an adapter to mount in the MNDC enclosure.

More later,   just some opinions,    Vic

[DavidH]

Sorry I didn't explain it too well. I've altered the circuit diagram and attached it to show you more clearly what I'm thinking.

There will be a breaker on the Classic's output to the battery but I'll run the wire out of the MNDC enclosure and attach it to the battery +ve terminal instead of making the connection within the enclosure like the previous diagram showed. This way I can put a fuse on the wire at the battery terminal.
Note: the wire size going to the battery +ve terminal should read 3 AWG and not 4 AWG.

[ClassicCrazy]

Why do you bring your Battery Positive charging Classic output  from the 60 amp breaker to the battery terminal - instead of just going to the bottom of the large inverter breaker ?  You don't need that extra wire run or another fuse in that line.

Also is that a jumper in the Classic negative connections between pv - and bat - ?  I believe they are internally connected so you don't need a jumper wire if that is what you were going to do.

Larry

[DavidH]

Larry, I'm not 100% sure whether that is a jumper or what - it's the circuit diagram that MidNite provides for that MNDC enclosure. If they are internally connected then that's good for me to know - thanks!

Ah, I had understood that a fuse was recommended along with the breaker as an added protection because it would blow faster than the breaker would disconnect. So is no fuse recommended on the battery's +ve terminal as long as I have the breakers in that circuit that MidNite has for the enclosure?

[mike90045]

.........Ah, I had understood that a fuse was recommended along with the breaker as an added protection because it would blow faster than the breaker would disconnect. So is no fuse recommended on the battery's +ve terminal as long as I have the breakers in that circuit that MidNite has for the enclosure?

Fuses & breakers are never fast enough to save the $$$ MOSFETS in gear.  They only prevent the wires from melting.

[DavidH]

Perfect, just having the breakers will make it easier then.