Sizing cable for forklift

I would be inclined to use a 50 amp MCB and cable to suit.

For a long hour load, I feel that a 45 amp MCB is cutting it too fine for a nameplate load of 44 amps.


If the charger is an electronic type then it will draw more amps at low input volts. At 207 volts I would expect an input of about 48/49 amps.


If the charger is a classic copper/iron type, then at 253 volts I would also expect an increased current draw.

Hi Broadgage,

thanks for your reply, just thinking out loud here I suppose I can use a 50mcb rather than a rcbo because the cable will be swa surface clipped and terminated into a rotary isolator at point of use, with the charger terminated to the rotary isolator too. Would the system still be compliant to the 18th edition this way??


Regards TS

According to table 4F1A 4mm² flex is rated at 30A, 6mm² at 39A and 10mm² at 53A - so 10mm² does seem plausible for a 44A load.


As for your 4mm² SWA being rated at 49A - I think that's for a 90 degree conductor rating - which is unlikely to be suitable for the terminals either of the MCB or the charger (see the notes against all the 90 degree tables in BS 7671). Unless you can show by some other means that the conductors won't exceed 70 degrees at the terminations the simplest approach is to use the 70 degree rated tables - in which case you'd need either 6mm² for 49A or 10mm² for 67A.(table 4D4A).


   - Andy.

i suspec there is nothing missed- flex cable supplied looks like it has some margin for  being used while coiled or other non ideal conditions . In your case it isn't, and won't be. I second rounding up to 50A and using 6mm though, this avoids a hot MCB and problems where your cable is bunched to get into the box.

Thanks for pointing out the round flex table this now makes alot more sense, I'm assuming that I should select a type C mcb for this too incase of inrush current as I have no experience in this and am unable to get hold of the manufacturer for guidance. 


Regards TS