Should outer shield of T&E enter back box?

[Halloway]

Hi,

I was replacing a faceplate earlier which was quite difficult due to the fact that there were three 2.5mm T&E cables entering the back box. All three cables had the outer shielding into the box but with no grommet on the access hole in the back box due to their being no room to fit one.

I was wondering: in such a situation is it better to have the outer shielding entering the back box with no grommet, or would it be better to strip the outer shield back to outside the back box, fit a grommet and then have the live, earth and neutral cables entering the back box?

To my mind, it would be better to strip back the outer shield and have a grommet. I suppose you could argue that the outer shield acts like a grommet, protecting the individual wires within, but an advantage to the former method would be that it would make routing of the LN&E wires easier within the back box, especially if there are three sets.

 

[EFLImpudence]

The sheath must enter the back box.

 

[JohnW2]

The sheath must enter the back box.

That is true, but I suppose that the OP was asking about the lesser of two evils, given that you would probably also say that the hole in the box "must have a grommet".

If one were faced with only those two options, I would have appreciable sympathy with the OP's viewpoint. However, the correct approach would obviously be a third option - namely to use two knockouts and hence have both grommets and the sheath entering the box - but that would probably be easier said than done with existing wiring/box.

Kind Regards, John

 

[EFLImpudence]

That is true, but I suppose that the OP was asking about the lesser of two evils, given that you would probably also say that the hole in the box "must have a grommet".

Why do you think I did not say that?
I don't consider it the lesser of two evils. The sheath must enter the back box.

If one were faced with only those two options, I would have appreciable sympathy with the OP's viewpoint.

I disagree.

However, the correct approach would obviously be a third option - namely to use two knockouts and hence have both grommets and the sheath entering the box - but that would probably be easier said than done with existing wiring/box.

Exactly.

 

[JohnW2]

Why do you think I did not say that? I don't consider it the lesser of two evils. The sheath must enter the back box.

Does that mean that you would be prepared to accept a situation in which the sheath entered the back box but without a grommet, or are you rejecting both of the options that the OP appears to be considering?

Exactly.

I would imagine that the OP also realises what the ('third') correct/ideal approach would be, so he has probably already considered that option.

Kind Regards, John

 

[Halloway]

I would imagine that the OP also realises what the ('third') correct/ideal approach would be, so he has probably already considered that option.

I did, but that would have required some chasing out which was outside the remit of the job!

 

[EFLImpudence]

Does that mean that you would be prepared to accept a situation in which the sheath entered the back box but without a grommet, or are you rejecting both of the options that the OP appears to be considering?

I am not sure what both options are.

I presumed he has the situation which is not easily changeable and is considering another one.

If the wires are held in masonry or filler then I do not consider a lot of work just to fit a grommet worth bothering with.

Squirt some silicone around the cables if it is thought beneficial.

 

[OwainDIYer]

The sheath must enter the back box.
The back box must have a grommet.
Even if the wires are held in filler there may still be building movement over time leading to chafing.

The 4th option is to enlarge the 20mm hole to a 25mm and fit a 25mm grommet. If done carefully the damage may be confined to the area around the box concealed by the accessory, and it saves chasing out the cables to go into two separate holes.

 

[JohnW2]

I am not sure what both options are. I presumed he has the situation which is not easily changeable and is considering another one.

Indeed, that's how I see it - he currently has the sheaths entering the box but no grommet. However, in what he went on to say, I thought he was asking a more general question about "in such a situation", not proposing that he should change what he has with the accessory in question.

If the wires are held in masonry or filler then I do not consider a lot of work just to fit a grommet worth bothering with. Squirt some silicone around the cables if it is thought beneficial.

I agree. Despite what OwainDIYer has said, I really don't think that, in the absence of a grommet, there is any significant risk of appreciable post-installation damage to a (sheathed) cable due to 'building movement'.

Kind Regards, John

 

[jj4091]

As far as I am aware fitting grommets is just considered good practice, not demanded by any regulation. Many people do not fit them, as you have found in your installation. There is a higher risk of causing a problem by trying to remove the outer sheath & fitting a grommet in the situation you have & as you have successfully fitted the socket I would leave well alone. The chances of there being any movement leading to chaffing must be miniscule.

 

[EFLImpudence]

However, in what he went on to say, I thought he was asking a more general question about "in such a situation", not proposing that he should change what he has with the accessory in question.

Well, yes so did I, but "such a situation" would surely not arise if you have a choice to begin with - use more holes.

 

[Halloway]

Thanks for your thoughts. There's is actually more wrong with the wiring in my living room than simply missing grommets. At some point, someone seems to have removed half of the socket 'locations' from the ring circuit and made them into spurs from the other sockets in the room. The reason for this I cannot fathom. I am mulling over returning the 'missing' sockets to the ring, which would remove the third cable from the two sockets I described in my first post, meaning a grommet could easily be fitted.

However, as you have undoubtedly already concluded, I am not an electrician and whilst changing a faceplate or two is within my limited abilities, I would be more circumspect about adding to or modifying ring circuits

 

[EFLImpudence]

I once had a building move and leave the back box behind.

 

[JohnW2]

Well, yes so did I, but "such a situation" would surely not arise if you have a choice to begin with - use more holes.

Yes, I agree that such a situation should not arise - at least, when one is starting from scratch.

Kind Regards, John

 

[EFLImpudence]

someone seems to have removed half of the socket 'locations' from the ring circuit and made them into spurs from the other sockets in the room.

Nothing wrong with that - if I understand correctly.