Can you fit 25mm conduit to a 20mm back box?

laurence1995

laurence1995

Hello,

Im really new to the world of conduit. I have some 25mm pvc conduit and cant for the life of me seem to fit back boxes with 25mm knockouts. Is there an adapter that fits a 25mm conduit in to a 20mm back box? Can i cut a 25mm hole in the back box? Do the 20mm male adapters allow for 25mm conduit to go into 20mm back boxes?
 
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Darkwood said:
You can get pvc reduces that allow 20mm to fit into 25mm setups, I am not sure but I assume you can get the reverse option too.
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Are you using 25mm for the amount of cables in the conduit? If so, it will be tricky to get them through anything smaller.
The hole in the adaptor through the threaded section will be even smaller than the conduit size. So even smaller than 20.

Either back boxes with 25mm holes already, drill the holes out bigger or reduce the conduit size.
 
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It might be tricky to "drill" (i.e. holesaw) out any exsiting knock-outs without it coming to a messy end as the cetre bit decides it is being knocked out. If you get a 25mm hole punch it can open out an existing 20mm hole much more easily and neater.
 
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As above, look at Q-max punches. I have a 20 and 25 and they are excellent bits of kit.
You drill a small hole, assemble it like a nut and bolt, tighten up and get a very clean hole.

(I often use the 20 punch, a galv coupler and bushes and a metal surface fused spur if adding outside lights and it’s a metal CU with no knockout in a convenient place)
 
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I have bought Q-max punches before from both of these places:
www.tooled-up.com

Q Max Sheet Metal Hole Punch Metric | Hole Punches

Buy Q Max Sheet Metal Hole Punch Metric and other Q Max Hole Punches at Tooled-Up.com. Fast Delivery.
www.tooled-up.com www.tooled-up.com

Toolbank Express — Toolbank Marketing

www.toolbank.com www.toolbank.com
However there are other places you might find them, not always as good value or in-stock:
stakesys.co.uk

Q-MAX Cutter Round - Metric

Q-MAX Cutter Round - MetricQ-Max Cutter for manually punching holes in sheet steel up to 1.6mm and aluminium up to 2.0mm. Very simple 100% British made tool that has been in production for over 50 years. To use, you simp
stakesys.co.uk stakesys.co.uk
 
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I don't think the OP has mentioned specifically which type of box is needed - PVC, steel surface or steel flush. Obviously if it's PVC, a holesaw or step drill goes through it in seconds with minimal risk of splitting, even if you're in the original 20mm entry. The Q-Max punch is best for steel, but if you have to use a holesaw and either the pilot drill or the edge of the saw is within a knockout, you can help prevent it detaching by clamping a small piece of plywood or similar behind it, although the clamp tends to get in the way of the drill.
 
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Not sure which way is required, 20 to 25 or 25 to 20, but a 25mm TRS gland often has the stuffing part with a 20mm thread. Discard the stuffing nut and the rubber compression seal, and you have a neat female 20mm to 25mm male adaptor.
 
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