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

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.

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

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.

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

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.

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.

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.

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

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.

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.

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.

In article ,
"Christian McArdle" says...
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.

I think you're going down a blind alley with that one ...

TLC do it. Useful for rectangular or unusual shaped cutouts.

Thought I knew their cat. intimately.;-)

http://www.tlc-direct.co.uk/Main_Ind...ets/index.html

Order code SR150. 5.75 for 5m.

Christian.

In article ,
Christian McArdle wrote:
TLC do it. Useful for rectangular or unusual shaped cutouts.

Thought I knew their cat. intimately.;-)

http://www.tlc-direct.co.uk/Main_Ind...ets/index.html

Order code SR150. 5.75 for 5m.

Thanks, Christian. But it's about twice the price of RS - and they do
other sizes too.

I've generally thought TLC to be good on a basket of prices but caught
them out on some other things too. Like their plug in octal relays. Anyone
who charges more than RS are taking the p**s. ;-)

--
*Why is it that to stop Windows 95, you have to click on "Start"?

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

I've generally thought TLC to be good on a basket of prices but caught
them out on some other things too. Like their plug in octal relays. Anyone
who charges more than RS are taking the p**s. ;-)

Unless that is where they buy them!

(Conversation witha supplier the other day... Me: "How much can you do
insert name of some laser/fax device here for?", Them: "nnn pounds
Sir", Me: "ah, I can get those for nn pounds from xyz", Them: "Oh...
ah... well in fact that is where we buy ours from so I guess you may as
well go straight to xyz!")

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/