Drilling holes in Fusebox knockouts?

[ppelec100]

I’ve always been alright with the knockouts provided for Fusebox consumer units but I’ve got a job coming up where I don’t want to use the large 32mm or 40mm knockouts.

I’ve got a 10 way board consumer unit to fit and the knockouts are so annoyingly spaced out, you could fit another 3 knockouts on the top if someone with common sense actually designed it.

I’ve never had to drill the knockouts and I want to know if I drill a 20mm hole centre of the 32mm knockout hole is the 32mm knockout going to drop out on me leaving me with a gaping hole I have to try and downsize or will I be okay if I drill it with low pressure and a sharp hole saw?

As they haven’t spaced it properly and I want to allow space for other knockouts in the future… what if I was to drill off centre so that my hole saw is cutting through the circular edge of the knockout will the knockout dropout?

 

[westward10]

Certain enclosures need considerable force to get the knockout out but I have never used Fusebox so can't comment. Have you used Fusebox before?

 

[Flanders]

Clamping a peace of wood inside. Before drilling may help prevent dislodging the knockout . I have not use fuse box so dont know how secure the knockouts are.

 

[SJD]

I've tried in the past with Fusebox, the knockouts came loose I'd either use a gland reducer, or put several cables in a larger size gland. Not much help if you want to gland a number of SWA cables, then perhaps fit a metal plate over the holes with the holes you want drilled or cut.

 

[ppelec100]

Certain enclosures need considerable force to get the knockout out but I have never used Fusebox so can't comment. Have you used Fusebox before?

I have used fusebox before but I’ve never had to drill the knockouts, whenever I’ve needed to drill them it would be on a surface with a plain section

 

[ppelec100]

I've tried in the past with Fusebox, the knockouts came loose I'd either use a gland reducer, or put several cables in a larger size gland. Not much help if you want to gland a number of SWA cables, then perhaps fit a metal plate over the holes with the holes you want drilled or cut.

Ahh that’s kind of annoying to hear, I’ve got what looks like 3 x 20mm swa and a 20mm flexi conduit gland to fit on the top surface.
I don’t understand why they would put such big knockouts with such ridiculous spacing.

With the metal plates, what did you use that’s convenient and won’t look so bad?

 

[nicebutdim]

I've tried in the past with Fusebox, the knockouts came loose I'd either use a gland reducer, or put several cables in a larger size gland. Not much help if you want to gland a number of SWA cables, then perhaps fit a metal plate over the holes with the holes you want drilled or cut.

I've drilled one Fusebox enclosure - think they have a 32mm knockout on the side and I needed to get a 25mm SWA gland in pretty much that very spot. Partially drilled the knockout with smooth cutting holesaw and had no issues (despite concerns to the contrary). This was a while back, but fairly certain there was a 32mm knockout on the left side of their 4 way mainswitch enclosure.

 

[SJD]

The only time I've used a metal plate, it was to line up holes with metal conduits in a service cupboard outside a flat, and didn't care what it looked like within reason.

More recently when I needed holes to align with some pyro glands and look ok I cut a set of new holes further forward than the knockouts.

I seem to recall older Fusebox units had smaller holes, but the last 2 or 3 years they got larger.

 

[SJD]

It occurs to me you could bolt a metal plate inside the box under the holes you want to partially drill then all you see is a few bolt heads.

 

[Mikegh]

You could fit a different CU for this job

 

[Flanders]

Another option might be it fit trunking along the top.

 

[Mikegh]

Another option might be it fit trunking along the top.

A new house

 

[pc1966]

I would be weary of fixing anything heavy/stiff to a knockout in case it breaks off later. For SWA you ought to have a CPC tail to a banjo or earthing nut anyway, but it still leaves the mechanical vulnerability.

A metal plate inside is an obvious solution, you could even have it fixed partly by the other 20mm fittings if glands are used and not grommets, etc, but you would only need a couple of short screws and nuts (ideally nylock or similar so they stay in place and don't loosen with vibration or thermal cycling).

Also @Flanders suggestion of some trunking is a good idea if you need a selection of cables, etc, and they are not suited to the standard layout. You can put a couple holes between them and some short 20mm or 25mm bushes and lock nuts for both cable protection and mechanical/electrical fixing of the trunking to the CU box.

A hole punch is really hand here as you can mark and pilot drill your hole locations, then G-clamp the CU & trunking together (or screw both to the wall as planned), and offer the male half of the punch to an existing knockout hole and place the female half on the trunking side, tighten the pulling bolt et voilà! a neat hole perfectly aligned for your bush to pass through. Repeat as needed...

 

[SparkySy]

I have done this using a galv conduit box lid on the underside of the hole. Knock out the original 32mm hole then fix the box lid in position with 2 m4 bolts and drill the size you require.
In some cases where I needed a bit more strength I have drilled an extra 2 fixing holes in the box lid and board.

 

[UNG]

A Q-Max cutter is useful for this sort of job as you only need to drill a 6 or 8mm hole for the bolt so it limits the stress on the knockout that a holesaw or step drill creates