I'm planning on fitting a new 17th edition metal CU and will fit glands to the mains tails but not sure if glands are necessary for the surface T&E coming in the CU from the top or would grommets be okay?

Obviously I need to make sure the grommets are a close fit on the cables but other than that I can't see why glands would be necessary. Is it to stop the cables being pulled out?

BTW I'm a retired time served sparky but never part P due to working in an industry that was exempt from this.

On 21/10/16 11:44, simon mitchelmore wrote:
I'm planning on fitting a new 17th edition metal CU and will fit glands to the mains tails but not sure if glands are necessary for the surface T&E coming in the CU from the top or would grommets be okay?

Obviously I need to make sure the grommets are a close fit on the cables but other than that I can't see why glands would be necessary. Is it to stop the cables being pulled out?

BTW I'm a retired time served sparky but never part P due to working in an industry that was exempt from this.


The top is supposed to meet IP4x (1mm probe cannot penetrate IIRC).

The classic solutions are to either fill up the gaps with silicon of
cable compound (TLC sell this) or conduit or run a bit of trunking over
the top.

I used short (8") stubs of conduit to take the cables above the ceiling,
but they are otherwise open at the top.

In article ,
Tim Watts wrote:
The top is supposed to meet IP4x (1mm probe cannot penetrate IIRC).

The classic solutions are to either fill up the gaps with silicon of
cable compound (TLC sell this) or conduit or run a bit of trunking over
the top.

I used short (8") stubs of conduit to take the cables above the ceiling,
but they are otherwise open at the top.

Mine is in the cellar - at the top of the stairs. On what was a plain
brick wall. So I simply dry lined the wall in that area, so all the cables
to the CU are concealed behind that.

--
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Dave Plowman London SW
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In article ,
simon mitchelmore writes:
I'm planning on fitting a new 17th edition metal CU and will fit glands to the mains tails but not sure if glands are necessary for the surface T&E coming in the CU from the top or would grommets be okay?

Note that both tails *must* enter through the same hole in a steel
case. (Ideally, so should the earth connection.) Otherwise you have
created a current transformer core around each cable which will
create eddie currents in the steel and heat it up when you draw
high current. When they go through the same hole, the magnetic
field cancels out and avoids this problem.

Obviously I need to make sure the grommets are a close fit on the cables but other than that I can't see why glands would be necessary. Is it to stop the cables being pulled out?

Not if they are fixed wiring which is fixed down.
If for some reason you have a flex coing out of the case, then that
would need a cable grip in the form of a gland.

BTW I'm a retired time served sparky but never part P due to working in an industry that was exempt from this.

Some metal 17th edition metal CU's (certainly Wylex) have an optional
grommet kit you can buy for sealing the cable entries.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:

both tails *must* enter through the same hole in a steel case.
(Ideally, so should the earth connection.) Otherwise you have created
a current transformer core around each cable which will create eddie
currents in the steel and heat it up when you draw high current.

I've heard that over the years, and it's what I would do, I'm sure that
one bloke's video doesn't prove that it's entirely wrong, but ...

https://youtu.be/hg5eZkq2KgE?t=1m54s

In article ,
Andrew Gabriel wrote:
Note that both tails *must* enter through the same hole in a steel
case. (Ideally, so should the earth connection.) Otherwise you have
created a current transformer core around each cable which will
create eddie currents in the steel and heat it up when you draw
high current. When they go through the same hole, the magnetic
field cancels out and avoids this problem.

I've seen this effect with long runs of steel conduit. I'm surprised it
would be noticeable with such a thin layer of steel?

--
*WHERE DO FOREST RANGERS GO TO "GET AWAY FROM IT ALL?"

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

Andy Burns wrote:

Andrew Gabriel wrote:

will create eddie currents in the steel and heat it up when you
draw high current.

one bloke's video doesn't prove that it's entirely wrong

Not sure why I phrased it like that, it doesn't prove it's wrong, in
fact it proves it does happen. What I meant was that it seems such a
minor effect, does it actually justify outlawing it?

On Sat, 22 Oct 2016 11:52:59 -0000 (UTC),
(Andrew Gabriel) wrote:

In article ,
simon mitchelmore writes:
I'm planning on fitting a new 17th edition metal CU and will fit glands to the mains tails but not sure if glands are necessary for the surface T&E coming in the CU from the top or would grommets be okay?

Note that both tails *must* enter through the same hole in a steel
case. (Ideally, so should the earth connection.) Otherwise you have
created a current transformer core around each cable which will
create eddie currents in the steel and heat it up when you draw
high current. When they go through the same hole, the magnetic
field cancels out and avoids this problem.

Obviously I need to make sure the grommets are a close fit on the cables but other than that I can't see why glands would be necessary. Is it to stop the cables being pulled out?

Not if they are fixed wiring which is fixed down.
If for some reason you have a flex coing out of the case, then that
would need a cable grip in the form of a gland.

BTW I'm a retired time served sparky but never part P due to working in an industry that was exempt from this.

Some metal 17th edition metal CU's (certainly Wylex) have an optional
grommet kit you can buy for sealing the cable entries.


https://www.tlc-direct.co.uk/Products/WKTKP40R32.html

is my choice of gland for the job.

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ARW wrote:

https://www.tlc-direct.co.uk/Products/WKTKP40R32.html
is my choice of gland for the job.

Bit more like it, rather than £15 for the Wylex one at screwfix.

On Sat, 22 Oct 2016 13:38:09 +0100, Andy Burns
wrote:

Andy Burns wrote:

Andrew Gabriel wrote:

will create eddie currents in the steel and heat it up when you
draw high current.

one bloke's video doesn't prove that it's entirely wrong

Not sure why I phrased it like that, it doesn't prove it's wrong, in
fact it proves it does happen. What I meant was that it seems such a
minor effect, does it actually justify outlawing it?


I was sent out to a job to redo the 70mm meter tails of a 3 phase DB
that had the tails passing through different holes. A ****ing great DB
with loads of load and other than this error been picked up on an
electrical inspection 30 years after it was installed they had never
had any problems.

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On Sat, 22 Oct 2016 15:12:24 +0100, Andy Burns
wrote:

ARW wrote:

https://www.tlc-direct.co.uk/Products/WKTKP40R32.html
is my choice of gland for the job.

Bit more like it, rather than £15 for the Wylex one at screwfix.

Wylex ramped up their prices a few years ago.

There is still this at screwfix

http://www.screwfix.com/p/horse/4879p

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In article ,
ARW wrote:
On Sat, 22 Oct 2016 13:38:09 +0100, Andy Burns
wrote:

Andy Burns wrote:

Andrew Gabriel wrote:

will create eddie currents in the steel and heat it up when you
draw high current.

one bloke's video doesn't prove that it's entirely wrong

Not sure why I phrased it like that, it doesn't prove it's wrong, in
fact it proves it does happen. What I meant was that it seems such a
minor effect, does it actually justify outlawing it?


I was sent out to a job to redo the 70mm meter tails of a 3 phase DB
that had the tails passing through different holes. A ****ing great DB
with loads of load and other than this error been picked up on an
electrical inspection 30 years after it was installed they had never
had any problems.

Did wonder about theory and practice.

--
*A fool and his money are soon partying *

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

On 22/10/16 15:13, ARW wrote:

I was sent out to a job to redo the 70mm meter tails of a 3 phase DB
that had the tails passing through different holes. A ****ing great DB
with loads of load and other than this error been picked up on an
electrical inspection 30 years after it was installed they had never
had any problems.

They didn't have a thin slot joining the holes by any chance?

Wish I'd read that about the tails having to use the same hole before I fitted it! I now have a snagging list item! I might even cut between the two holes as the tails are so rigid and such a pain to unthread.

It's all working except for a suspected 'borrowed neutral' which trips both ELCB's on the stairs lighting (which I will sort).

Thanks all for the useful info.

On Sat, 22 Oct 2016 18:40:33 +0100, Tim Watts
wrote:

On 22/10/16 15:13, ARW wrote:

I was sent out to a job to redo the 70mm meter tails of a 3 phase DB
that had the tails passing through different holes. A ****ing great DB
with loads of load and other than this error been picked up on an
electrical inspection 30 years after it was installed they had never
had any problems.

They didn't have a thin slot joining the holes by any chance?

No. They passed through bush couplers. 70mm is a ******* to terminate
into the main switch.


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On 23/10/16 17:17, ARW wrote:
On Sat, 22 Oct 2016 18:40:33 +0100, Tim Watts
wrote:

On 22/10/16 15:13, ARW wrote:

I was sent out to a job to redo the 70mm meter tails of a 3 phase DB
that had the tails passing through different holes. A ****ing great DB
with loads of load and other than this error been picked up on an
electrical inspection 30 years after it was installed they had never
had any problems.

They didn't have a thin slot joining the holes by any chance?

No. They passed through bush couplers. 70mm is a ******* to terminate
into the main switch.


Just wondered - that was a solution in one of my dad's engineering books
to avoid the eddy currents.