Adding plastic T box into metal conduit

[thespaceman]

I need to add two sockets to an existing ring main. Metal conduit was fitted originally and and earth wire runs within the conduit. I need to cut into the conduit to run the wires for the new sockets.

Can I use a plastic T conduit box for this and if so should I fix earth clamps to the two cut ends of the metal conduit and join with earth wire?

Or can only a metal conduit box be used here? The conduit is under floor.

 

[breezer]

you will have to cut the conduit in half, find out it wont fit a plastic conduit box, realisie you have just sawn through the cables, and give up.

there is always an alternative

 

[GaryMo]

Metal conduit box!

 

[breezer]

Metal conduit box!

Can I use a plastic T conduit box for this

how is he going to thread it if its fixed? this i gotta see

 

[GaryMo]

Metal conduit box!

Can I use a plastic T conduit box for this

how is he going to thread it if its fixed? this i gotta see

Is it fixed? The OP didn't say it was. If it is fixed is it fixed by saddles?
Are there no other boxes in the length he's going to break into?
Is it all buried in concrete or under floorboards?

Either way, as I said - metal conduit box. You don't use plastic conduit boxes with metal conduit. It's not push-fit!

 

[Lectrician]

Metal conduit box!

Can I use a plastic T conduit box for this

how is he going to thread it if its fixed? this i gotta see

A running coupler or two.......

Admittadly, not really a DIY challange.

The OP also does not state if it is under/in a suspended timber floor, or in a screed.

 

[GaryMo]

The OP also does not state if it is under/in a suspended timber floor, or in a screed.

Exactly.

Talking of running couplings......some 19 years ago on my very first day at work I was asked to do my first running coupling!

 

[securespark]

The conduit is under floor.

I take that to mean it is acessible, ie under a suspended timber floor.

 

[ColJack]

how is he going to thread it if its fixed? this i gotta see

View media item 4387
one of these with a conduit die set...
available to rent from many places, or one in the back of my van..

 

[breezer]

coljack, what that then? never seen one of them.

But guys, you are all missing the point.

thespaceman, knows (or doesnt know how / have the kit) that he cant add a metal box, so he wants plastic.

My point is there has to be a DIY alternative that thespaceman can do. I am curios whay there is an earth wire when its a steell conduit.

we really need more info

 

[GaryMo]

coljack, what that then? never seen one of them.

It's a powered die set. It will thread the end of a conduit or pipe with much less effort and restriction than a standard set of stocks.

But guys, you are all missing the point.

thespaceman, knows (or doesnt know how / have the kit) that he cant add a metal box, so he wants plastic.

If he hasn't got the knowledge or required tools then he needs to look for an alternative idea or employ somebody with the necessary skills.

I am curios whay there is an earth wire when its a steell conduit.

Perhaps the installer chose to run one and not rely upon the integrity of the conduit as a cpc? Many people run seperate cpc's when installing steel conduit or trunking.

 

[Lectrician]

Is there a circluar box in the conduit run already anywhere?

Take the lid off, and fit a plastic circular terminal (single entry) box ontop, with a hole in the back.

Then either use some 20mm plastic conduit, or a TRS gland. You can get plain ended TRS glands to glue into the conduit spout, or use a female conduit adaptor and a threaded TRS gland.




Those electric threaders are less labour intensive, but still take the same sort of time.

They are widely used by installers of compressed air pipwork etc.

 

[thespaceman]

wow this has raised a lot of debate.

The conduit is under a suspended floor and is attached by crampets/saddles to the underside of the joists. The conduit itself is a straight run with bends horizontal and vertical up to the sockets.

So from what you are saying the conduit would have to be cut on a straight and I would need to use straight couplings in order to allow the the T to be screwed in? I've never quite understood how these conduits are assembled when there are bends etc preventing rotation.

I had a look at one of the original sockets today are there are no earth wires in the conduit as I had wrongly assumed.

So it's probably important to continue the metal conduit with a metal junction. Does this also mean that I would have to use metal to my new sockets? Or is there a method of earthing to the conduit with a screw or clamp etc?

I've decided to let a professional help with this one as I'm slightly out of my depth and don't have the tools etc for threading the ends.

Thanks for the help so far

 

[plugwash]

Generally you would use a circular T box for a T junction. If there is enough clearance the box itself could be joined using a running joint, if there is not enough clearance for that the conduit could be bent away from the wall, the box screwed on and a running coupler used the other side. If there is not enough give in the conduit to do that two running couplers could be used.

For a running joint a much longer thread than usual is put on the end of one peice of conduit. The other peice is threaded normally. Then a locknut is put on the peice with a long thread, then the box or coupler is scrwed on to the peice with a long thread much further than usual.. Then the box or coupler is screwed accross so it is screwed to both peices of conduit. Finally the locknut is screwed tight against the box or coupler to make the joint more solid.

A conduit T box should have enough space inside to terminal block to new cable though pulling in continuous runs is considered preferable.

 

[thespaceman]

Well the electrician came round today and finished the job. Instead of breaking the ring he's fed the two sockets back to the consumer unit and run them as a radial circuit.

I wished I had though of that!