Discussion
Electricity is much like water. Although they don't like one another.
If you imagine water flowing in a pipe network. The voltage is the same as the force of the pump pushing the water. The current [amps] is the flow of water past any given point. The resistance is related to the diameter of the pipe - the smaller the diameter, the higher the resistance.
If you imagine water flowing in a pipe network. The voltage is the same as the force of the pump pushing the water. The current [amps] is the flow of water past any given point. The resistance is related to the diameter of the pipe - the smaller the diameter, the higher the resistance.
No you cannot assume that a cable used for AC will be OK for DC without knowing the distances involved.
You need to worry about voltage drop and power generation in the cable, google for DC wire table or similar. You'll find that you need thicker cables than you expect.
Lots of info on this sort of thing on green sites because of people running 12V photovoltaics or low voltage lighting.
As an example table see http://www.windsun.com/Hardware/Wire_Table.htm
You need to worry about voltage drop and power generation in the cable, google for DC wire table or similar. You'll find that you need thicker cables than you expect.
Lots of info on this sort of thing on green sites because of people running 12V photovoltaics or low voltage lighting.
As an example table see http://www.windsun.com/Hardware/Wire_Table.htm
TooLateForAName said:
No you cannot assume that a cable used for AC will be OK for DC without knowing the distances involved.
You need to worry about voltage drop and power generation in the cable, google for DC wire table or similar. You'll find that you need thicker cables than you expect.
Lots of info on this sort of thing on green sites because of people running 12V photovoltaics or low voltage lighting.
As an example table see http://www.windsun.com/Hardware/Wire_Table.htm
The op didn't mention anything about DC! I know what you are thinknig, he will be using it for some sort of 12v DC lighting but its only 12v after the transformer so any cable up to that will be 230v anyway. You need to worry about voltage drop and power generation in the cable, google for DC wire table or similar. You'll find that you need thicker cables than you expect.
Lots of info on this sort of thing on green sites because of people running 12V photovoltaics or low voltage lighting.
As an example table see http://www.windsun.com/Hardware/Wire_Table.htm
GC8 said:
Allow me to expand on my question. I have a quantity of 25mm2 cable and Id like to make some slightly longer than average jump leads (4m). Would I be correct in assuming that the cable can carry a similar amperage when used in a 12v application, as it can in a 230v/240v one?
25mm squared? 
you could probably power London through that. Or did you mean 2.5mm sqaured? 25mm may be ok, I dont know much about it, but I don't think 2.5mm would do the job for jump leads, on start up you are looking at drawing 500-700 amps.Road2Ruin said:
GC8 said:
Allow me to expand on my question. I have a quantity of 25mm2 cable and Id like to make some slightly longer than average jump leads (4m). Would I be correct in assuming that the cable can carry a similar amperage when used in a 12v application, as it can in a 230v/240v one?
25mm squared? you could probably power London through that. Or did you mean 2.5mm sqaured? 25mm may be ok, I dont know much about it, but I don't think 2.5mm would do the job for jump leads, on start up you are looking at drawing 500-700 amps.GC8 said:
Allow me to expand on my question. I have a quantity of 25mm2 cable and Id like to make some slightly longer than average jump leads (4m). Would I be correct in assuming that the cable can carry a similar amperage when used in a 12v application, as it can in a 230v/240v one?
It'll carry the current OK (especially as it's only for a short time and you'll be there to watch it if it starts to melt!) but you will get some volt drop - don't forget that for 4 metre jump leads the total length is 8 metres. I reckon you'll lose about 1V.ETA: If 3.6 meters is enough there are some 600A leads here for next to nothing: http://www.amazon.co.uk/Silverline-594260-600-Jump...
Edited by Deva Link on Monday 21st December 15:42
GC8 said:
Its meter tail cable, so Id guess seven strand, but Im not certain. 16mm2 cable seems to be used on 'best' supermarket quality leads, although thats only good enough for a real 60a-80a, I think.
Welding cable would be best, but Id like to use what I have to hand.
Relevant table from 16th edition of the wiring regs. http://www.batt.co.uk/upload/files/table4h1abs6007...Welding cable would be best, but Id like to use what I have to hand.
It suggests 25mm as rated as 97amps single phase ac or dc. This must be for a standard pvc sheathed cable as we use this gauge in TRS for 125a temporary single and three phase cabling without issue.
Its probably not good enough for a serious jump-start either.
Are the meter tails you have flexible enough not to cause issues with good connection to batteries when jump-starting ? Wouldn't something with same cross section but more strands be better anyway ?
Thanks for the replies. I hadnt realised the decent welding cable was so inexpensive. The jump leads linked to were indeed quite cheap. Most jump leads are usually high on thick insulation and thin on copper wire though. Even 16mm2 is good and thick for jump leads and its thicker than most youll find.
I will replace the inflexible meter cable with welding cable, I think.
I will replace the inflexible meter cable with welding cable, I think.
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