Advise on hole cutting - steel consumer unit

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Hello,

I'm installing a new consumer unit in my flat for one of my Part P qualifying jobs.

It's a concrete building with all the wiring in conduit and MICC.

I've got a new steel Wilex CU which has various round knock-outs for the cabling, but a few of them don't line up with the existing conduit etc.... some line up half on / half off the knock outs.

Does anyone know of a tried and tested way of hole cutting across knock outs without "knocking them out".

Also can anyone recommend a good set of hole cutters (metric and imperial) for the job.

Any advise would be greatly appreciated,

Thanks,

Al

 

[UNG]

Clamp 2 pieces of wood 1 inside and 1 outside of the box and use a hole saw to drill through the wood and box where you need the holes ( no need to drill through the wood inside the box that provides support to the knock outs)

I use Starrett holesaws not cheap but they outlast others I've used

 

[scanner]

Genius !

Thanks UNG...

I'm off to buy some clamps and some hole saws.

Have a good day !

Al

 

[UNG]

Good to see someone is happy, glad I could help

 

[ian.settle1]

You may have a problem as some knockouts which have 2 small pieces of metal holding knockout to the CU, drill them out and knockout will come out as well.

You would therefore have to put a metal plate acoss the top on the outside of CU.

 

[UNG]

Thats why you clamp the wood in place to stop the holesaw ripping the knockouts out

 

[wattsup]

various methods, I usually fix 2 x 2 galv / plastic / trunkings under/side/top. bush through to existing knockouts, spacing locknut between

 

[Des 56]

various methods, I usually fix 2 x 2 galv / plastic / trunkings under/side/top. bush through to existing knockouts, spacing locknut between

This is the method I have seen countless times and advise to use
Depending on the spacing and quantity of the conduits coming through the top,try and pick these up directly,fit 2x2 galv trunking underneath,drilling holes to suit the pipes and the dist board ,bush and locknut with a locknut between to keep the board and the trunking slightly apart

 

[bugsy]

I'd also go with a length of trunking, having said that I've never tried the other method

 

[ian.settle1]

Thats why you clamp the wood in place to stop the holesaw ripping the knockouts out

What I was refering to was not ripping the knockout out but when the hole is cut and the hole cut happens overlap the part of the knockout which is attached to the CU the knockout will come out

 

[scanner]

various methods, I usually fix 2 x 2 galv / plastic / trunkings under/side/top. bush through to existing knockouts, spacing locknut between

This is the method I have seen countless times and advise to use
Depending on the spacing and quantity of the conduits coming through the top,try and pick these up directly,fit 2x2 galv trunking underneath,drilling holes to suit the pipes and the dist board ,bush and locknut with a locknut between to keep the board and the trunking slightly apart

Hi Wassup + Des 56,

I'm trying to visualize this...

So you're cutting the trunking to use as a plate to keep the integrity of the CU ?

IE. attaching the trunking to the CU using bushes and locknuts to non knock out overlapping holes, then drilling the remaining holes regardless of whether the knockouts come out, as you'll be leaving the conduit / plate in situ.

Also, what's the advantage of keeping the board and trunking slightly apart with the locknut between ?

Thanks a lot,

Al

 

[pennywise]

They mean drill holes on one side of the trunking that match your knock outs on the CU. Then cut holes on the other side of the trunking that match the positions of the MI and conduits. you sandwich the trunking between the two, the cables pass through the trunking and then into the CU via the bushed knock outs. It's just so you don't have to have the norse of trying to drill holes between knock outs on the CU. You want to keep the trunking slightly apart from the CU with lock nuts because its a pain to get the lid on the trunking if it's butted up too close to the board.

 

[scanner]

They mean drill holes on one side of the trunking that match your knock outs on the CU. Then cut holes on the other side of the trunking that match the positions of the MI and conduits. you sandwich the trunking between the two, the cables pass through the trunking and then into the CU via the bushed knock outs. It's just so you don't have to have the norse of trying to drill holes between knock outs on the CU. You want to keep the trunking slightly apart from the CU with lock nuts because its a pain to get the lid on the trunking if it's butted up too close to the board.

Right,

I'm with you pennywise,

Thanks for that.

But that's my problem...

It's a damn tight fit as it is and I don't have the extra space for the trunking.

I going to go with UNG's clamp and wood block method.

If a knockout does come out I'll have to attach a plate and re-drill....

I don't recall being taught there was anything wrong with this approach per se, but I'm guessing it'd be ok if the CU integrity and IP standards were maintained... I'll ask elecsa tomorrow.

Thanks for all the replies...

what a nice community !

Al

 

[UNG]

What I was refering to was not ripping the knockout out but when the hole is cut and the hole cut happens overlap the part of the knockout which is attached to the CU the knockout will come out

You make it sound like it is a certainty that the knockout will fall out I have done this loads of times are never had a problem

 

[Davey101]

You make it sound like it is a certainty that the knockout will fall out I have done this loads of times are never had a problem

It is a certainty if you drill out one of the 'tabs' holding the knockout in place. It wont stay in with only one side holding it. Some knockouts will stay in no matter how much stick you give them, some will fal out if you look at them the wrong way.

 

[UNG]

Once the conduit bushes clamp the knockouts in place there won't be a problem

 

[gaffer]

Sometimes wish the manufacturers didnt put those stupid knock outs in and just let us drill the holes where we want them.

 

[UNG]

Especially when the knock out is a different size to what you want

 

[PJK]

Ialso use the 2 x 2 plastic trunking on the top of the CU. It is a very good way of complying with the required IP rating for a horizontal top surface.

 

[Davey101]

Once the conduit bushes clamp the knockouts in place there won't be a problem

Agreed