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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Ring Circuit - steel knockout boxes/grommets
As we're having our lounge replastered, I'm taking the opportunity to
extend the ring and add a couple of extra double sockets in convenient places. I've done this before and I'm quite happy with the wiring side of things but, in the past, I've always used the plastic surface-mount boxes to do this. As I'm going to be adding the sockets between the time the old plaster comes off and the new plaster goes on, I want to use steel knockout boxes cut into the brickwork to give a flush finish matching the other sockets in the room. Never having used the steel boxes before, I understand that you are supposed to put a grommet on the knockout to protect the cable. Looking on the screwfix site they have 'open' and 'closed' 20mm PVC grommets - the images look identical, so what's the difference and is there an advantage in using one type over the other? Many Thanks Perry |
#2
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Looking on the screwfix site they have 'open' and 'closed' 20mm PVC
grommets - the images look identical, so what's the difference and is there an advantage in using one type over the other? The closed ones are "filled in". You need to puncture a hole for the cable to go through if there isn't one already. This means that the hole is exactly the right size for the cable, though. Christian. |
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On Tue, 7 Jun 2005 10:31:20 +0100, "Christian McArdle"
waxed lyrical about: Looking on the screwfix site they have 'open' and 'closed' 20mm PVC grommets - the images look identical, so what's the difference and is there an advantage in using one type over the other? The closed ones are "filled in". You need to puncture a hole for the cable to go through if there isn't one already. This means that the hole is exactly the right size for the cable, though. Christian. Thanks, that makes sense - they've obviously got the wrong image on the site. Perry |
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Christian McArdle wrote:
Looking on the screwfix site they have 'open' and 'closed' 20mm PVC grommets - the images look identical, so what's the difference and is there an advantage in using one type over the other? The closed ones are "filled in". You need to puncture a hole for the cable to go through if there isn't one already. This means that the hole is exactly the right size for the cable, though. Funnily enough I took 'open' and 'closed' to mean something rather different:- Closed - the grommet is a continuous toroid, but still has a hole in the middle for the cable. Open - the grommet is actually just a length of U shaped rubber but is shaped in a circle so the ends butt together. Open grommets are much easier to get into the hole in the box than are closed grommets and, as long as they're the right size, protect the cable very nearly as well. I expect you're right but I think (as someone else said) 'blind' would be easier to understand for 'closed'. -- Chris Green |
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In article ,
wrote: Funnily enough I took 'open' and 'closed' to mean something rather different:- Closed - the grommet is a continuous toroid, but still has a hole in the middle for the cable. Open - the grommet is actually just a length of U shaped rubber but is shaped in a circle so the ends butt together. IIRC, grommet strip - but you'd need to go to somewhere like RS for this. Open grommets are much easier to get into the hole in the box than are closed grommets and, as long as they're the right size, protect the cable very nearly as well. They also pull/push out more easily. ;-) -- *I'm not being rude. You're just insignificant Dave Plowman London SW To e-mail, change noise into sound. |
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IIRC, grommet strip - but you'd need to go to somewhere like RS for this.
TLC do it. Useful for rectangular or unusual shaped cutouts. Christian. |
#7
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In article ,
"Christian McArdle" writes: IIRC, grommet strip - but you'd need to go to somewhere like RS for this. TLC do it. Useful for rectangular or unusual shaped cutouts. The sheath stripped from T&E by running a knife down the side of the earth conductor (like what you're not supposed to do;-) makes excellent grommet strip, and is guaranteed not to react with the cable sheath of course. On straight edges, it needs glueing on, but so does real grommet strip. Different sized T&E gives grommet strip suitable for different thickness metalwork. Another form of grommet strip is to take a grommet for a larger hole and cut a piece out. I usually end up doing this for the smaller holes in architrave back boxes. The trick is to not cut out quite enough, so the grommet is held in place with some compression force. You could glue the ends if you wanted, but I've never found it necessary. -- Andrew Gabriel |
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In article ,
Christian McArdle wrote: IIRC, grommet strip - but you'd need to go to somewhere like RS for this. TLC do it. Useful for rectangular or unusual shaped cutouts. Thought I knew their cat. intimately.;-) Where about - it's not with the ordinary grommets. Which I notice they call open and blind. -- *Pride is what we have. Vanity is what others have. Dave Plowman London SW To e-mail, change noise into sound. |
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I expect you're right but I think (as someone else said) 'blind' would
be easier to understand for 'closed'. That's also a term I've heard used for closed, but I don't think it is easier to understand! Blind for me means someone/thing that can't see. And all grommits are somewhat challenged in the seeing department, AFAICT. Christian. |
#10
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In article ,
Christian McArdle wrote: That's also a term I've heard used for closed, but I don't think it is easier to understand! Blind for me means someone/thing that can't see. And all grommits are somewhat challenged in the seeing department, AFAICT. A blind stops you seeing through a window. You can see through an open grommet, but not a blind one. -- *Time is the best teacher; unfortunately it kills all its students. Dave Plowman London SW To e-mail, change noise into sound. |
#11
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A blind stops you seeing through a window. You can see through an open
grommet, but not a blind one. So you could call it a "curtains" grommit as well? Especially a pre cut one. Christian. |
#12
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#13
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In article ,
Perry Gunn wrote: Looking on the screwfix site they have 'open' and 'closed' 20mm PVC grommets - the images look identical, so what's the difference and is there an advantage in using one type over the other? The other name for closed is 'blind'. It is a disk rather than a ring, as it were. You simply fold it in half and use sidecutters to make a slit while not cutting into the 'ring' part. Since you'll be making good afterwards, either type will do. -- *Arkansas State Motto: Don't Ask, Don't Tell, Don't Laugh. Dave Plowman London SW To e-mail, change noise into sound. |
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