1/0 wire

[transmitterdan]

If a 1/0 cable became loose it would probably start a fire before it came off altogether. The fears about doubling cables are not born out by real life examples.

Paralleling cable of equal length is an acceptable practice. Make sure to terminate them correctly and secure the lugs properly. If you can properly crimp AWG 4 cable but not 1/0 then better to go with parallel smaller cables. Don't use the hammer crimpers.

It is not a good idea to put 2 wires into one crimp lug. The crimp lug probably will not crimp right as it is designed for a circular bundle of wires. Better to use the correct size lug on each wire IMO.

[masonc]

Originally Posted by pcmm

This is done all the time. I just finished doing a tour of a large data center (their generators are powered by V 16 diesels! ) and all 8 of their starter circuits are wired this way, but with 4/0 AWG cables. the stuff is just massive ( yeah I'm a nerd and notice that kind of stuff!!)

For clarity, although I'm reminded the National Electrical Code does not apply to boats, paralleled cabling is not just done all the time, there is no other way to wire large current applications. We commonly run 4 x 500mcm per phase. You can't easily bend cables above 750mcm, even with hydraulic bending and they wouldn't go through conduit.
However, code requires the smallest allowable parallel conductor set to be 1/0.

[Wotname]

Originally Posted by DotDun

The REAL answer is YES! It's done generally to increase current carrying capacity of a circuit.

Without more information, one has to assume that 1/0 is what the application requires (~285a). (2) 4awg in parallel will yield ~320a. With that said, most would opt for the 1/0 cable due to ease of installation/management.

But contrary to what's been stated, there is nothing unsafe, temporary, or wrong about paralleling cables to gain ampacity.

Dot Dun and others who are happy with the practice of paralleling cable to gain ampacity, please consider some sample circuits below.

For this exercise, the load draws 30 amps when active. Cct A is safe, cct B is safe unless one cable goes open circuit, then it becomes very unsafe.

If the load is inactive (turned off) and low resistance fault develops on one cable as in cct C, the circuit is safe, the cables can carry the fault current until the breaker trips. But should a similar low resistance fault occur as in cct D, then the arrangement in unsafe, the single conductor will in likelihood fail (burn) before the breaker trips.

Now these are only sample circuits but they demonstrate why twin smaller conductors can't be considered safe in some scenarios.

To repeat an earlier post, it boils down to risk assessment and risk management.
Would I use parallel cables - yes in some circumstance and no in others.

[transmitterdan]

I think cct D is unlikely to happen if the termination is good. However we are not taking about paralleling AWG 14 wire but AWG 4 wire. I think that makes the probability of a cct D scenario virtually nil. And the scenario ignores how cct D came to be in that state. One wire somehow worked itself loose and came all the way off but did not magically start a fire in the process.

Who has a real world documented example of paralleling larger wires that came to a bad end? Could that same thing happen on a boat?

If in doubt then it would be ok to parallel extra third wire for added redundancy.

[DotDun]

Originally Posted by smac999

as already mentioned there are reasons not too. if one cable breaks, or say is left disconnected by mistake. you'll now have 300a going through a single 4awg. and nobody would ever know or relize untill it burns. where as if the 1/0 comes off it won't work and you'd notice right away.

So, what is your recommendation for an application that requires more than 445a that the largest cable available (4/0) can deliver? Do your concerns disappear?

Like I stated, paralleling cables require extra 'management', your imagined concerns fall into that realm and must be dealt with.

[double u]

"... if one cable breaks... you'll now have 300a going through a single 4awg. and nobody would ever know or relize untill it burns."

if this logic were true then one shouldn't have ANY wires at all on the boat: they might get chafed through halfway & now you have...

[jonasaberg]

I did not find this thread earlier today and started a new one where I got to know about this earlier thread.

I wrote a quick summary, and for those interested it is found here:
http://www.cruisersforum.com/forums/...ml#post2397121

[Leakie Marine]

If you are working with AC then doubling would help take advantage of skin effect because you have more surface area where the current tends to flow. I would still make sure the single conductor was capable of carrying the rating of the breaker.

https://en.wikipedia.org/wiki/Skin_effect