Cable sizing

[DEVLEC]

Hi Guys
I have been arguing with a guy at work about some supplies he's been installing.
He has installed two 16 amp three phase sockets using 4mm swa clipped and in trenches of about 30 meters he's protected it with a 32 mcb.
The swa terminates in a switched fused isolator with 32 A fuses in. Out of the fused terminals he's used 2.5 singles to the sockets which are about 500mm away.
I said the singles should be 4mm or the fuses should be 16 A.
to protect the 2.5 s and 16 A sockets.
He was originally going to use 2.5 swa with a 32 A mcb to supply this installation his argument was the machines wont pull more than 5 amps each. Any comments please just needed to vent my spleen thanks

 

[nickblake]

Well if his maximum demand is only 5 amps perphase why did he select a 32 amp MCB when he could use 10 amp depending on the inrush current you are correct in saying that the fuses should be 16 / 20 amp but as ive said could easily be 10 amp .(10 amp due to the max demand being so close to the MCB / Fuse rating dont want it to get hot )

 

[Guest123]

A 16A rated socket outlet protected by a 32A fuse doesn't sit quite right with me. Even though the downstream load is as you say rated at 5A so can draw no more, it isn't a fixed load and something else could be plugged in at any time by anyone which may cause a problem!

 

[nickblake]

A 16A rated socket outlet protected by a 32A fuse doesn't sit quite right with me. Even though the downstream load is as you say rated at 5A so can draw no more, it isn't a fixed load and something else could be plugged in at any time by anyone which may cause a problem!

i missed that one very sore eyes to night after doing a BBq for a load of brownies ,yes i know its october and the bbq should be in the shed but were in wales and it always feels like summer

 

[Guest123]

yes i know its october and the bbq should be in the shed but were in wales and it always feels like summer

Too right! we only have the one season so anytime is appropriate for any activity.

 

[davelerave]

16a sockets should be fused correctly i would say - it may not cause a problem here with dedicated loads


if they were SP sockets -appliances could easily be added on later to leads etc. resulting in overcurrents and 'disconnection times' not being met with a 32amp

 

[DEVLEC]

I totaly agree with you guys.
I found another machine supplied by 2.5 swa on a 32a mcb.
HMMMM

 

[Guest123]

Got to be careful here as 3 or 4 core 2.5mm XLPE SWA (90degreesC) has a tabulated CCC (It) of 32A+ in some cases but that is pushing it to say the least IMO.

PVC SWA on the other hand doesn't. I think we all agree that 2.5 should not be protected by a 32A MCB as in most cases with factors applied the formula Iz>In>Ib is not adhered to.

It's 20A or possibly 25A max for me.

Is this particular machine on a plug and socket arrangement also???

 

[DEVLEC]

Hi Lenny
No its standard PVC SWA clipped direct, wired straight to the machines isolator.

 

[nickblake]

Ill be honest and agree with lenny i would never use any higher than 20 amp mcb on a 2.5mm .twe swa or other reason being its what happens after its installed , as i have said in a post in our area they have installed 200 of insulation over the cables whic changes the installation methods to 103 which means the cables current carrying capacity reduces dramatically so if you designe for worst case values ratings you cant go wrong ,having seen a family wiped out in a house fire i feel its the best way to work

 

[DEVLEC]

I agree I always go on the side of caution and step up sizes just in case. Especially in industry , Insulation wont be a problem but you never know what will be added to the machine in the future.