Earthing back boxes and socket outlets

[mike]

Just came to fit some socket outlets from Toolstation and realised the faceplate screws aren't connected to earth.

They're the top ones in this pic:

Older MK version with earth connection is below.

I thought all sockets followed the MK pattern with the result that using either the earth connection on the faceplate or the earth connection in the back box would result in everything being connected to earth. But if someone made the earth connection to the back box on the Toolstation version, any connected appliance (double insulation and plastic earth prongs aside) wouldn't be earthed. Is that right? Is this something new? Or something cheap?

[polygonum]

I thought that each connection had to be made separately, and relying on the faceplate being in contact with the back box was a no-no. Even if, as in the MK case, it might actually be connected.

[fred]

In article , mike writes

If we simplify the situation by assuming a surface mounted plastic patress then we have exposed metal parts (fixing screws) that can readily come into contact with the basic insulation on the conductors (the brown and blue cores) when the box is assembled.

Rules are that exposed metal parts need to be separated from live conductors by 2 layers of insulation (double insulated)[1] or if there is only one layer of insulation be earthed.

Given that, I can't see how these parts can be compliant.

Given the supplier I am not that shocked, it wouldn't be the first time a buyer has bought on cost only to be bitten in the arse when they find out they have worthless shit in the warehouse.

Oooh, pass me another budget lasagne Neddy . . . .

[1] Special case of reinforced insulation set aside for this example

[John Rumm]

As you have seen, not always...

No, because the circuit earth wires will always be connected to the earth terminal on the socket face plate. You would not simply terminate the circuit earth wires on the backbox and rely on that to make an earth connection to the backbox.

With a "normal" socket that has earthed screw holes the reverse situation is allowable - i.e. you can re;y on them to earth the backbox (assuming it has at least one fixed tag), however good practice would suggest adding a separate fly lead between circuit terminal and the earth terminal on the back box.

No and yes.

[Dave Plowman (News)]

It's best practice to run an earth wire between the socket and earth terminal on a metal back box. That's why it's there.

[Lobster]

Don't think I've ever seen them before - I always assumed the earthed screw holes were mandatory

So, if you have sockets with earthed screw holes does that mean you actually don't need the fly lead twixt socket and backbox? I thought it must be a belt-and-braces thing or something, but didn't think you could just do away with the flylead?

[John Rumm]

IIUC, so long as the box has at least one fixed lug, then you can do without the discrete fly lead.

[charles]

If the socket happend to be be hanging loose, how do you get earth continuity?

[mike]

So "no" in theory but "yes" in practice because there will inevitably be cases where people connect it to the back box earth.

If everything is reliably earthed via the socket screw in the situation you describe, how would it be any less reliable if the earth were connected to the back box rather than the face plate?

[ARW]

If the socket has just one earthed eyelet and this is at the adjustable lug side of the backbox then you also need to fit the flylead.

[John Rumm]

The circuit earth wires are always connected directly to the socket. So even with the socket completely disconnected from its backbox (which may be plastic remember), it still is both earthed, and providing earth continuity.

[ARW]

Best practice and electricians? Pull the other one:-).

I fit the flyleads in older houses where there are damp problems and where the spec says I have to.

Any competent DIYer should be fitting the flylead as they are not on price.

The sockets in question were brought to the attention of this group last year by SteveWalker. They are Toolstation's "Contractor Pack", marked HLM.

[John Rumm]

Excluding cases conduit/sheath/armour earthing is in use it seems relatively unlikely - its not as if its any easier to connect two wires to the box and four to the socket... I have seen countless examples of no flying lead betwixt socket and box, but don't recall ever seeing the being being used at a primary connection point.

Because in reality its a less reliable connection...

While not desirable, an unearthed backbox is unlikely to kill you, but an unearthed socket might.

Imagine a situation where some one is decorating and has release socket screws to get paper etc behind the faceplate. Anything plugged into that socket *must* still be earthed, but whether the box still is in those circumstances is less important.

[Frank Erskine]

Very often the earth lug on the back box isn't large enough to take three 2.5mm wires.

[Dave Plowman (News)]

;-) But if I were an electrician I'd make sure the terminal screws were left loose to.

Quite.

Seems they saved 0.0001p by not running the earth strip to the screw holes.

[ARW]

That's not always true. Sometimes they overtighten the screws to see if they can snap off half of the screws head. It's a fine balancing act to decide which one to do.

I would not normally buy electrical stuff from Toolstation. Steve Walkers post guaranteed that I would avoid those sockets should I ever have to buy from there.

[Dave Plowman (News)]

For myself, I tend to buy the fittings I like the look of, since you're likely to have to look at them for a long long time. Which usually means not the cheapest I can find. ;-)

[ARW]

That's how I choose my girlfriends.

[SteveW]

Thank you, I was just about to search for my original post, but I'll not bother now!

SteveW

[Windmill]

Most of the sockets I've seen which were wired relatively recently have a squashed-flat loop in the earth wire to allow it to fit into the back box terminal, but the wire then continues on to the earth terminal on the socket. All one piece of wire so less risk of an open earth connection if there are loosely-fastened screws in back box and/or faceplate. I had assumed that was more or less a standard for a professional installation.