Grommets or conduit in metal back boxes?

[gembrain]

I've seen a few comments on failed installs because of lack of grommets - although apparently not a specific requirement as such.

Is oval conduit plastered into chase and fed a little into the back box OK or does one HAVE to cut it just short of the the box and fit a grommet?

Granted it's a sharp edge but where the cable comes in at the top of the conduit is the same.

Thanks

 

[kingeri]

Shoot the messenger trolling more like . This is ELECSA advice NOT MINE for fs sake , I fit the dam things as ive said .' no wonder so many just read mostly or bin this site & move on .

Congratulations.

 

[ferg]

This is purely from my somewhat suspect memory, but here goes anyway.
I believe there was an electrical fire at a nursing home a few years back at a metal DB.
The cause was a cable chafing against a knockout and the cupboard where the db was located was used for storage including flamable liquids.

The recommendations following it were obvious.

I think this might have been it. Nursing home blaze which killed 14 elderly people was 'totally avoidable' - Daily Record
BBC News - Rosepark care home deaths 'preventable' inquiry finds

But please don't take my memory as being accurate.

 

[gembrain]

And it seemed such a simple question to me.......!!! Hmmmm...

I definitely get that grommets are best but I must admit after 60 odd posts I'm still not clear whether having the oval conduit running into the box without a grommet is a pass, a fail, or just room for improvement!

Reading some other threads elsewhere it looks like it can be anything from a Code 1 (!!!) to a code 4 or fine as it is.

Apologies if anyone's blood pressure got raised as a result of the thread - I think I'm just bemused!

 

[ferg]

Well if the pvc oval is inside the box then you have no worries about the cable chafing against the knockout.
If the oval is clean at the end and there is no tension between it and the cable then I see no issue with the oval damaging the cable inside the box.

I must admit I just scanned the whole thread briefly and saw the grommet or no grommet argument before my first post.

 

[Risteard]

Just to make the discussion a little more fruity..... what do we make of this?

View attachment 19230

LOL. Surprised they didn't add a female bush too!

 

[MDJ]

. This is ELECSA advice NOT MINE for fs sake , I fit the dam things as ive said .' no wonder so many just read mostly or bin this site & move on .

I refuse to believe ELECSA recommend installing cables into metal enclosures without protection, impossible, give me the name of the person from ELECSA who advised you about this and I will phone them up with reg numbers suggesting they are wrong and send an e-mail to their main head office recommending they retrain all their operatives, absolutely appalling advice IMO.

 

[Tuttle]

Shoot the messenger trolling more like . This is ELECSA advice NOT MINE for fs sake , I fit the dam things as ive said .' no wonder so many just read mostly or bin this site & move on .

I had a discussion with an ELECSA assessor about this, he said that there is nothing in the regs that says that grommets must be fitted, he also said that he wouldn't suggest that I stop fitting them.

The edges of the boxes are sharp, you need something to stop them damaging the cable.


Edit:

Just to give a bit more background about the discussion I had ... we were talking about earth tails to back boxes, and whether or not they were required, and he used grommets as another example of something that doesn't have to be fitted but you wouldn't want to not fit.

He definitely didn't suggest that they shouldn't be fitted.

 

[MDJ]

I had a discussion with an ELECSA assessor about this, he said that there is nothing in the regs that says that grommets must be fitted, he also said that he wouldn't suggest that I stop fitting them.

The edges of the boxes are sharp, you need something to stop them damaging the cable.


Edit:

Just to give a bit more background about the discussion I had ... we were talking about earth tails to back boxes, and whether or not they were required, and he used grommets as another example of something that doesn't have to be fitted but you wouldn't want to not fit.

He definitely didn't suggest that they shouldn't be fitted.

I think your point is very valid and correct, however I think to comply with section 522 of the regs regarding mechanical protection and stresses covering your backside by adding a grommet, coupler,adaptor or grommet strip for just examples will help you adhere to the regs, and although in theory a double insulated cable entering a metal enclosure if held correctly to avoid possible mechanical damage would be adequate it's just easier to protect the cable where it enters the box and I like your wording on the subject which is much more sensible than the other drivel spouted out by one member here, only enthusiasts and not electricians would consider no protection in metal enclosures IMHO.

 

[telectrix]

.an exception is the 1/2" back boxes for switches, where the oval cable entry hole is chamfered so as to have no sharp edges.

 

[Rockingit]

.an exception is the 1/2" back boxes for switches, where the oval cable entry hole is chamfered so as to have no sharp edges.

Does anyone still use those???

 

[MDJ]

I haven't for donkey's years TBH, usually a 25mm2 box or a 35mm2 box if I know a dimmer is going in, that said I suspect they are still in use by a lot out there, I see them on the shelves in wholesalers and Tels right they are rounded off so the metal is safe and there,s no risk to the cable, funnily enough though you can get a 20mm2 grommet in one, but there's no room for the cable :lol: