Cables too big for bus bars/breakers

[pablo]

Hi all,

Thank you for reading.  I have a bunch of solar power equipment that I purchased, but my solar guy bailed on me so I am DIYing.  I have installed small systems in the past, but generally I would call myself a beginner/intermediate in terms of knowledge. 

I have 4/0 cable running from my array to the house.  How do I connect this cable to my MNPV6-250?   I believe the largest bus bar connection is 1/0.  I am not finding specs for the output lug on the the DIN rail, but it looks about 1/0 as well.    I will need electrical cable reducers on both ends of my cable run, for both the combiner box connections and the inverter connections.   Ideas?
thank you

[ClassicCrazy]

That is very large cable - what voltage and current are you running from your solar array ? How many panels do you have ?

Usually these days a design would be to run panels in series to get higher voltage to reduce that wire size. Then the MPPT controller will drop the voltage down to match the battery voltage.

Larry

[pablo]

It sure is big and bulky and cumbersome, but it was already in place and buried in the ground from a former low voltage (12 volt) system with a long run...

So I elected to use it to save time and money, both of which are in short supply    I have two Solar World 285 Watt, 31 Volt panels and a Outback flexmax60 MPTT controller.  The cable is aluminum so I guess that added to the size. 

[CDN-VT]

No worries Is the cable in conduit & pictures always help explain..
So for Voltage drop they used hard strand commercial cable  , I understand .
So tell us your everything of distance & everything , spend time to explain everything , we have Very smart folks here & they will always help ! They helped me , So Seee !!

I need help

VT  & good folks here , just explain ALL makes it so much easier than pulling teeth

[ClassicCrazy]

How about something like this for 4/0 to smaller cable ? Use antioxidant on the aluminum cable connection and torque well and recheck later.  This one says only 2/0 but maybe a larger one is available.
http://www.galco.com/buy/Marathon-Special-Products/1323572?source=googleshopping&gclid=Cj0KEQjw-Mm6BRDTpaLgj6K04KsBEiQA5f20E6oQ3vJYgSkzC2jT6kyvwRwztNTus9IBI8V_jWyJersaAqRY8P8HAQ

Larry

[TomW]

How about something like this for 4/0 to smaller cable ? Use antioxidant on the aluminum cable connection and torque well and recheck later.  This one says only 2/0 but maybe a larger one is available.
http://www.galco.com/buy/Marathon-Special-Products/1323572?source=googleshopping&gclid=Cj0KEQjw-Mm6BRDTpaLgj6K04KsBEiQA5f20E6oQ3vJYgSkzC2jT6kyvwRwztNTus9IBI8V_jWyJersaAqRY8P8HAQ

Larry

I have used those and they come in literally huge sizes. Very easy to mount and use.

Tom

[pablo]

Thanks for the suggestions!   What about something like this?

It's a compression fitting - tin plated copper.  Goes from 4/0 to #2, but it says for stranded wire.  My wire is solid.  I wonder if that would make a difference?   Can I mix AL with CU?

The cable is not in conduit - direct burial. 

I'm working on the design for putting my system together.  The best resources I have found for how to wire it up are the user manuals for the combiner box and the charge controller.  I tried to find some solar power books to help, but they all get very abstract when it comes to wiring...  When I have my design done, I will post and ask for a review.

[Westbranch]

look at this reference for a miriad of options, a page or so down there is apic of 2 copper ended lgs, thye may be better for you...https://www.google.ca/search?q=lugs+ferrules&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiqt6Sqr5HNAhWKFR4KHaPhD7kQsAQILQ&biw=1366&bih=608

[pablo]

I guess part of my concern with using reducers is resistance.  In going from 4/0 to say 4 AWG, what happens to the current?  What is the voltage drop?  Will heat be a problem?  Doesn't this type of connection create some type of electrical bottle-neck? 

[ClassicCrazy]

Since your  main wire is oversized as long as the connnector or reducer has good connections you shouldn't have any resistance problems if you size the smaller wire going to your combiner at least for the minimum called for in specs.

Larry

[Vic]

Thanks for the suggestions!   What about something like this?

It's a compression fitting - tin plated copper.  Goes from 4/0 to #2, but it says for stranded wire.  My wire is solid.  I wonder if that would make a difference?   Can I mix AL with CU?

The cable is not in conduit - direct burial. 

Hi pablo,

OK,  #4/0 AWG cable IS HUGE.   Running this huge cable that is SOLID in conduit is extremely difficult,  and therefore quite uncommon,  in my experience.

Are you absolutely certain that this cable is 4/0 and solid ??  Not to insult you,  but this seems beyond an extreme combination.

The Box Lugs in those terminal blocks are almost always used with stranded cable.  Often the range of conductor size is limited for the use of solid conductors.

FWIW,   Vic

[pablo]

Thanks for checking Vic!  Gosh, I feel like an idiot now.  I just went out and double checked and it is 1/0.  My AWOL solar guy had wanted me to use 4/0 for battery to inverter connection and I must have switched oughts in my poor dilapidated brain. 

So that should make things easier.   Thanks again for taking the risk of insulting me. 

[pablo]

I cut off a chunk of the 1/0 (by the way a ratcheted pipe cutter works great for this) and tested it in my combiner box.  It fits into the bus bars and the rail lug, but not into the breaker switch. 

Why not just shave down the diameter of the aluminum at the end of the cable to make it fit?  wouldn't that be better for electrical flow than using an adaptor and smaller wire? 

[TomW]

Why not just shave down the diameter of the aluminum at the end of the cable to make it fit?  wouldn't that be better for electrical flow than using an adaptor and smaller wire?

Not sure of the long term effects of just lopping off some of the diameter but it should not affect resistance / voltage drop.

wire resistance is rated by diameter and length so a stubby reduction will not be an issue and it seems certainly less than a lug, terminal block, etc.

Be careful not to nick solid wire it can break at a nick easily.

If I did this I would use a dremel tool or somesuch to carefully shave off diameter all around with a rounded shoulder between full size and reduced end (Not square)

Just from here.

Tom

[Vic]

   ...     I just went out and double checked and it is 1/0.  So that should make things easier   ...

Thanks pablo,  for checking.    1/0 solid should be easier to handle than  4/0.

Reducing the diameter may be OK,   but,  as Tom mentioned,  be careful to not nick the conductor.

This solid,  large cable  is very stiff,  as you know.  This can cause the cable to put forces on the connection points,  that are not normal.   These unusual forces could possibly create stresses or issues for the busbar,  or circuit breaker.  Not to make too big a deal about this.   Just try to dress this large cable,   trying so that it will relax  just where it needs to be  --  this is more difficult to do with stiff,  large diameter cable.  The busbar for your Combiner is probably the most sensitive to forces applied to the  buss and the breakers by very stiff cable.  This could be the most difficult place to get the 1/0 cable dressed,  so that it rests in the correct place for its cable connector.

Good Luck,   Vic