How does each “fix” of the electrics work?

[Adsibob]

Spending a small fortune on light switches and sockets. Also designed quite a complicated lighting scheme with lots of two way switching and in some cases three way switching. All the two way switching have a dimmer switch at one point in each circuit. There is three floors of a 5 bed house to do, all from scratch.

Presumably the light switches don’t get installed at first fix, they go in at the second fix together with the light fittings. But if that’s correct, how does the electrician make sure he has got all the wiring right? If a mistake isn’t discovered until 2nd fix, isn’t it too late by then to fix it?

[Onoff]

1st fix the cables and back boxes go in.  All gets plastered. Cable is coiled up and stuffed in the boxes. Plasterer will gleefully fill these up with his goop for you to dig out later. You either accept some digging out or you can get various posh little inserts to protect the back boxes or even make your own. I've seen the cable ends wrapped in cling film and even tin foil! Cling film isn't a bad shout if you've cables poking out the ceiling. Gets "tricky" when you move away from the traditional single centre light in each room to multiple downlighters. Probably better then to plaster then hole saw out and fish the cables through. That needs planning! Tbh a good spread should cope with whatever but they prefer a clear run. 

 

2nd fix sockets and plates go on. Then it all gets DEAD tested. Hugely important step as opposed to banging them all in and switching on! Dead testing should show up any faults long before power is applied.

 

Use a reputable sparks for a start. Stick to safe zones for all your drops. Even mark on the plasterboard the safe zones if you want. It's not unheard of but rare to get a "dodgy" cable off a reel of twin and earth. So buy decent cable. Damage is usually down to a nail, screw, pinch, plasterers trowel. Then it's down to how it's been run as to whether it's easy to replace. Running in plastic conduit in the walls is dirt cheap. Through joists then keep it up out of the way of plasterboard screws hitting it, (50mm). Imagine if it would "pull through" easily later on.

 

Even if plastered in at worst it's going to be one run that might need digging out...or one ceiling coming down! ?

[nod]

Most electrician write on the ends of the wires as they go It’s quite unusual for an electrician to miss anything 

Certainly on a house 

[MikeSharp01]

Once you have been over your design with a fine tooth comb your electrician can do the cabling at first fix and then return to it for second fix and anything they missed will be their need to fix, which at that point can be quite expensive - or you use radio switches to get around the problems which as @nod says are/is rare. You need to think about how the multiway switching will work with dimmers and if its complex you might like to consider radial wiring where for the lighting where everything comes back to a central point and the interconnections are made there that way, provided you have installed enough 'ways' to the boxes you can wire it how you like back at the box. Also radial allows you to have complex controls in the middle and simple switches at the boxes.

[ProDave]

With a plasterboarded, timber framed house, the wiring is usually done before the plasterboard goes on.

 

This creates a problem.  All you can do is leave the cables in a bundle where they want to emerge, and HOPE whoever fits the plasterboard does at least drill a hole and poke them through.  If the gods are shining on you, you will get a good boarder who will cut the back box holes in exactly the right place and size. More often the boarder will just drill a hole at a completely random height and poke your cables through.

 

So 1 1/2 fix is go back after the plasterboard is on, cut all the back box holes, leaving the spare holes the boarder drilled at completely the wrong height for someone else to fill up.  Then go fishing for the missing ones that got left behind the boards and hope you remembered sufficiently well where they were so you can find them first try.

 

Worst case (yes this really happened) I drilled a hole for a downlight, no cable.  Drilled the next one. No cable.  Luckily the floor was up above so I went to look, and the cable I had left looping from light to light in the kitchen had been unclipped pulled out from where it passed through the joists and coiled up in the middle of the room.

 

If this is your own build them make sure your boarders don't miss any cables and at least drill a hole at the correct height and place to pass them through.

 

TIP:  2 way switching needs intermediate switches.  Wtth a lot of them, you might find yourself needing a norlam and an intermediate switch on the same plate.  Have a look at the Click Mode switches, they let you unscrew the switch module and swap them around so you can make up unusual configurations.

[Bitpipe]

Our wonderful electrician wired the full 4 floors of our house flawlessly and seems to have a photographic memory of where everything is. A few years after moving in we were finally installing a light fitting in the hall but it would not work - quick call and he instructed which wall switch to remove and reconnect the live he'd disconnected for safety. 

 

He also used metal back boxes everywhere and the boarders cut them perfectly so no surprises when it came to second fix - we had a few cables for LED strips that needed to be fished out. 

 

So get a decent electrician and decent plastering team and all will be well.

 

Worst case I learned you can get a hole cutter, chop out a disc of plastered wall, fix/find what you need do, glue a batten behind it and glue the cut disc back on. Smear of caulk around the cut line and a lick of paint - like it never happened.

[Nickfromwales]

43 minutes ago, Bitpipe said:

Our wonderful electrician

Captain S is on site for me atm, only have to tell him complex things once. Bliss.

 

44 minutes ago, Bitpipe said:

So get a decent electrician

Yup. So very refreshing to meet someone like-minded who can just be left to work to his own devices, without babysitting. ? 

[Nickfromwales]

We're just in the middle of dry testing a sizeable project before boarding commences. All back boxes in, all loop-ins Wago'd together and insulation resistance testing galore to be completed before a single board goes over anything / anywhere major. I like to back roll the cables at the boxes so they cannot be pushed back into the grommet and become lost in the studwork / void. Some spreads, sadly, have the brain power of a plant, and I've been back to jobs where the cables have been pushed back into the voids around the boxes with zero regard as to how they are to be retrieved. Spreads like to shoot straight across a board when skimming, so they can get things nice and flat, so anything protruding is fair game.

[Temp]

 

11 hours ago, Adsibob said:

if that’s correct, how does the electrician make sure he has got all the wiring right?

 

I got a copy of my house plans and marked them up with switch/dimmer and socket positions for the electrician. You can also write on the walls. 

[Pocster]

4 hours ago, Onoff said:

Hugely important step as opposed to banging them all in and switching on! Dead testing should show up any faults long before power is applied.

I assumed my sparky would do this but he didn’t . His logic is if there’s faulty wiring you’re going to find it either way . So he just wired everything up and powered on . I did all the wiring so tbh was expecting an issue like a screw through a cable - nothing - perfect

 

I’m so multi talented even I’m surprised  ?

Edited August 2, 2021 by pocster

[Temp]

50 minutes ago, Nickfromwales said:

I've been back to jobs where the cables have been pushed back into the voids around the boxes with zero regard as to how they are to be retrieved.

 

Some 40 years ago when I was kid I got a summer job with an electrician helping to wire up a 6-8 storey office block in Staines. All the floors were identical so we dropped off the same number of switches and sockets on each floor at the start of the day. Finished fitting them on one floor and had one light switch left over.  Took us hours to find out where the missing one should go because the plasterer had totally filled the back box and polished it over.  No plans and no mobile phones to take pictures back then so we had to go up and down and rely on memory to try and figure out where the missing one should go.  Once we had narrowed it down to a wall I volunteered to go down the fire escape get his metal detector to find it. Don't bother he said and proceeded to stab the wall with a screwdriver over an area of about two square meters while muttering under his breath.. "That will teach the F&%$£s.. "

 

Learned a lot that week...

 

Always leave about three feet of wire sticking out after first fix - later you can cut it to a more suitable length, collect the cuttings and burn off the plastic for the copper.

 

How to avoid having to carry massive rolls of left over carpet down 6 floors - just make sure the car park below is empty before you push it off the fire escape. 

 

Always check an electricians references - at another site the recently hired electrician just failed to turn up one day. They eventually found he had just been pushing short lengths of wire into the conduit and fitting sockets. It was the same at the distribution board, if you pulled a wire just a short length came out!

 

 

[Adsibob]

All very helpful, thanks. My architect has amended his lighting schematic to show which switches work which lights, so this will hopefully make things easier. And glad I don't have to risk the finish on my switch plates by having them installed at first fix just to test.

Although the drawings are now super clear, I don't envy the electrician. Complex job!

[TonyT]

Make sure you have metal boxes fitted to walls, simply because if you have flat plate accessories( sockets and switches) they look daft with the gap off the wall.

 

35mm boxes as a minimum allow plenty of room for sockets, usb sockets etc with 47mm for cooker switches, outlets etc.