30AMP wire

So a customer of mine (I work in a local parts store here in Australia) is building an RB26DET into R31 and obviously needs upgraded fuel pumps, he is running a surge tank and I believe an 040 in tank pump. Now the issue is he has just informed me that the pumps need 30 amp wire but he only purchased 15 amp twin core. Now he has told me that instead of buying new wire (his argument is he has already spent way too much money) he is just going to twist each end of the 15 amp twin core to make one "30 amp" wire, now I tried to explain how that will not work but he is a qualified mechanic and I'm just a parts guy so he believes it will work. Could anyone please expand on this and tell me if I am wrong.

It will 'work' but is less than ideal.

What usually happens on high current circuits is its not so much the wire, but the terminals the wire goes onto that will fail first. Even when using less than perfect wire size.

And the 30a pump will probably only be 20a normally, and raise to 30a when the fuel pressure raises because of boost. Realistically, you will only be in that high boost period for a few seconds in a row.

I wouldnt do it like he is. But if his connections are sound, then it will probably work.

Volt drop will be an issue though, so he may loose an extra volt because of the wire run length and size.

Thanks heaps for the reply I will let him know that it will but may run into the issues you have stated later on.

Yup, it will work but seems daft to do so when it's a fraction of the cost of the whole job, won't work as neatly as a proper single wire, is going to be a cow to terminate and there are other applications where he could use that wire and will now have to buy more anyway.

BTW, that he is a mechanic doesn't mean much on it's own - I'm a trained 'A' Grade and many I've known have trouble with the difference between volts and amps.

Wonder what he is doing for the ground side?

Gord I believe he is doing the exact same thing for ground