Armoured cable to garage

21 Apr 2023
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United Kingdom
Hi, Planning to run armoured cable from house to garage, what size cable do I need. The garage is only 3metres away form house consumer unit but want 4 sockets for power tools, lights led and welder 180amp working safely any help much appreciated.
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Welding set output is normally 25 volt plus 1 volt for every 25 amp so 180 amp at 32 volt so needs around 25 amp the in rush depends on welding set, inverter sets are a lot better, so as @Dan Can says 6 mm² is likely enough, but the volt drop and prospective short circuit current should be calculated first, easy enough to say a 40 amp overload will do, but with a non inverter welder inrush could be a problem, and a type C could be required so loop impedance needs to be less than 0.55 Ω since we have no reading we have no way of knowing if within limits.
For that length may as well Run 10mm it's not going to cost much more. Best go to a wholesaler for it though. At some point a car charger could be installed?
You may need to notify your electricity supplier that you will be using a welder.

This is the application form for a new supply but it highlights the issue with disturbing loads, so called because the inrush current can affect your neighbour's supply.

welder app.jpg
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I did look at heat pumps, most seem to be inverter drives, so no real inrush, I know using a clamp on does not really give starting current as many are too slow responding, a B32 will trip at 5 times so 160 amp, and I have used a clamp on which set to show max showed 100 amp but it tripped the MCB so clearly taking a lot more.

I had a small welder with 13 amp plug, and it would trip a B20 but OK with a B32, much depends on how the amps are set, those with a moveable iron core often you can wind out the core, switch on, then set to current required, but if switched on without winding it out first, it would trip the supply.

But we have an inverter welder 160 amp and never had a problem on 13 amp supply.

Today we fit SPD so they should get rid of spikes, but son has lost loads of LED lamps, and myself very few, which could well be some one using a welding set near him, but near impossible to prove.

The form seems rather dated, my fridge and freezer are both three phase, and both are inverter controlled, but connect to a single phase supply, and set the energy meter to record max current use and one can see it show 140 watt each time it hits the defrost cycle, but the older single phase units would hit around 7 amp each time the motor started, so far more disruptive.

Basic fact is a welder is not a domestic appliance, but if it does not trip a B16 MCB/RCBO unlikely to cause a problem.

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