Mixing cable sizes

Submitted: Thursday, Jan 30, 2014 at 22:41
ThreadID: 106020 Views:2141 Replies:3 FollowUps:4
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G'day all,
If I use the wire calculator ( http://www.bulkwire.com/wireresistance.asp ) and it shows that I need (or can get away with!) 1/0 b&s cable and I already have a 4 b&s cable in place, can I run an additional 2 b&s cable to achieve the same capacity as a 1 b&s cable ie does 4 b&s + 2 b&s = 1/0 b&s. Obviously the additional cable will be connected to the same +i've and -i've as the original cable.
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Reply By: Brian 01 - Thursday, Jan 30, 2014 at 22:52

Thursday, Jan 30, 2014 at 22:52
Close enough to a 1/0 and about 30% bigger than a 1.
You mentioned both of those, so I covered them both.
AnswerID: 525438

Reply By: Member - Ian G (NSW) - Thursday, Jan 30, 2014 at 23:39

Thursday, Jan 30, 2014 at 23:39
Many thanks Brian.
I should have proof read my post.
I meant 1/0 b&s not 1 b&s
AnswerID: 525441

Follow Up By: oldtrack123 - Friday, Jan 31, 2014 at 13:41

Friday, Jan 31, 2014 at 13:41
Hi Ian

Paralleling the same sized cables is usually ok, PROVIDED they are the same length

But when parallelling diffferent sized cables it is possible for one to carry more than it's share of the current
That may be a problem if the max current is right on the combined rated currents of each cable

Perhaps when you finish the job run them at full load for say 5<10mins & see how hot they get compared to each other

FollowupID: 807406

Reply By: Member - Rob D (NSW) - Friday, Jan 31, 2014 at 14:32

Friday, Jan 31, 2014 at 14:32
1 B&S has a cross sectional area (CSA) of 42.41 square mm, 2 B&S has a CSA of 33.63 square mm and 4 B&S has a CSA of 21.15 square mm.

Thus a 2 B&S plus a 4 B&S has a combined CSA of 33.63 plus 21.15 or 54.78 square mm, so it has a larger CSA than the 1 B&S. Current carrying capacity is not rated solely on CSA, it depends on the cooling ability (surface area) of the cable and airflow as well.

You need to be careful how you protect the cables by fuses or circuit breakers.
Fuses and circuit breakers are there to protect the cables, to stop them conducting too much current, overheating and then causing a fire.

If for example you have two wires rated at 10A each in parallel, then the combination has a current rating of 20 amps.

If you protect the circuit with a single 20A fuse or circuit breaker and one of the cables has its insulation worn off on the chassis then that cable will draw far more than it is rated for and may overheat and cause a fire.

In your case for chassis wiring 1 B&S is rated at 211A, 2 B&S is rated at 181A and 4 B&S is rated at 135A.

I hope this helps.
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AnswerID: 525495

Follow Up By: oldtrack123 - Friday, Jan 31, 2014 at 16:44

Friday, Jan 31, 2014 at 16:44
HI Rob
Some very good points in your post
Parallelling cables should be a last resort ,IMHO

Lots of potential problems with load sharing ,protection, etc

The same goes for paralleling ANY currrent carrying components OR sources

No matter what voltage or power type [Ac OR DC]
FollowupID: 807427

Follow Up By: Member - Toyocrusa (NSW) - Saturday, Feb 01, 2014 at 20:40

Saturday, Feb 01, 2014 at 20:40
Just wonder PeterQ. My 2500watt inverter has two + and two - connection points for the 12v side and is supplied with two of each + and - cables. Is that normal ? Thanks, Bob.
FollowupID: 807504

Follow Up By: oldtrack123 - Saturday, Feb 01, 2014 at 20:54

Saturday, Feb 01, 2014 at 20:54
HI Toyo
I think you will find both the PO & both the Negs are on common busbar /terminal blocks
So smaller cables can be used for flexabilty
One pair of pos & neg to each group
BUT again best they are ALL kept the SAME length ,so they SHARE the input current equally !!,

FollowupID: 807506

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