Daisy Chain Mains Extensions

[gramophone1]

Is it safe to daisy chain mains extensions ?

[kellys_eye]

Short answer - no.

Longer answer - depends on the current being drawn.

Personally I wouldn't do it under any circumstances.

[paulsherwin]

It's not considered good practice, but I do it for low current appliances in certain circumstances. You should be very wary of doing it for things like electric fires though.

[broadgage]

Best avoided, and certainly not to be recommended for non technical persons.
Not however absolutely prohibited if done by someone who understands the potential risks.

Extreme sounding case that was actually safe, numerous 4 way extensions daisy chained so as to give nearly 100 outlets from a single 13 amp socket. The total loading was about 8 amps and consisted entirely of Christmas lights.

Another example, 3 long single outlet extension leads used end to end for a total length of nearly 150 metres. Supply from a portable generator of very limited capacity. Load about 2 amps and double insulated.
The long run being required to keep the generator out of earshot.

In general though, best avoided.

[The Philpott]

The switched dizzy boards need watching as to keep costs down there is a temptation to use poor quality switches, which are prone to welding themselves closed. A big fluorescent tube is an example of something that would cause this. Nearly got zapped once because of this.

My main concern would be if a lot are used for something that needs an earth, the contacts on most extension leads are quite poor. This isn't much of a problem with the power contacts as a bad one would lead to a thing not working. The earth, if disconnected, however wouldn't be noticed until it was too late.

[OscarFoxtrot]

The problem with long or thin leads (especially something like 150 metres!) is the earth fault loop impedance. The more the impedance the less fault current will flow, and the slower the fuse or circuit breaker will operate. For sockets and other equipment which could be tightly grasped 0.4s disconnection time is required.

The longer time the electricity flows through you the more likely you are to die.

PAT test guidelines for extension leads with 13A fuse:

1.25mm² 12m max length
1.5mm² 15m max length
2.5mm² 25m max length (and you won't get 2.5mm flex into a 13 amp plug, you'll need to use BS4343 'ceeform' or 'commando' connectors)

They mustn't be daisy-chained to longer lengths.

By fitting a lower current fuse, you could in theory increase the cable length proportionally. The RCD removes the concern over earth fault loop impedance, but you may in theory end up with a short on the cable which takes long enough to blow the fuse that the cable gets damaged.

[extrapolated from Andrew Gabriel at news:uk.d-i-y)

[broadgage]

The 150 metre example that I mentioned was from a small portable generator. Worrying about earth loop impedance is bit pointless in such circumstances since the generator cant supply enough current to open any likely size fuse or MCB.

[gramophone1]

Thank you for the replies.

I have ran out of sockets for my hifi, and the idea was to daisy chain from existing mains extension.
I think it best, I don't attempt it at all

[M0FYA Andy]

I do it on my computer installation, so it's a 'semi-permanent' set-up with a number of daisy-chained extensions along the back of my computer bench and down onto the floor to another table with my A3 printer.
I'm fully aware that it is 'frowned on' as a practice, but as a computer installation comprises a lot of low-current loads (each with a suitable fuse in the plug) I've not been able to think of a reason 'why not?'. I've certainly never had any trouble, touch wood.

Andy

[kalee20]

Apart from the uncertainty of the earth connection, I'd have said yes it is safe! But Daisy-chained only, not branched (which would be very easy to overload).

The worst that could happen is that you get excessive voltage drop, meaning the equipment at the end would receive less than normal voltage. A lot of stuff would draw correspondingly less current. Some modern stuff might draw more current, self-compensating. Some older items, with tapped mains transformers, could be manually adjusted.

What is important, whatever - is to ensure excess extension lead is not left coiled up. Warmth generated in the cable needs to be spread out to dissipate, not concentrated in a tight knot with no airflow, else the temperature could rise enough to start melting insulation.

[IanBland]

I think personally that the dangers are overstated. However many things you plug into things, you've got the 13A fuse in the first plug preventing a current overload of the whole network. Every 4 or 6 way block will be itself rated to 13A.

I personally find it a bit silly that we go to the trouble of having plugtop fusing (and saying how much safer we are than countries that don't) then saying it's terribly dangerous to expect it to actually work as designed.

There may well be a fault current issue with long extension leads, but in a domestic enviroment with a meter or two of cable on a 4 way block I would not worry at all.

[Graham G3ZVT]

An even more important consideration is, if the extension leads are the type on a reel, you must uncoil the reel completely. A coiled up cable can become dangerously hot, at a fraction of its rated current capacity.

[GrimJosef]

Originally Posted by IanBland

I personally find it a bit silly that we go to the trouble of having plugtop fusing (and saying how much safer we are than countries that don't) then saying it's terribly dangerous to expect it to actually work as designed.

There may well be a fault current issue with long extension leads, but in a domestic enviroment with a meter or two of cable on a 4 way block I would not worry at all.

I agree with you Ian. I do take merlinmaxwell's point about a long series of plug-to-socket connections increasing the risk of a poor earth contact though. In this respect daisy-chaining may be more dangerous than branching. If I should need, say, 16 outlets then I could achieve that by branching four four-way leads from one more four-way and no outlet would be more than one plug-and-socket joint from the wall plug. If instead I were to daisy-chain them then the final four in the chain would have four plug-and-socket joints between them and the wall.

Cheers,

GJ

[PaulM]

I think that for the general public, the idea that daisy-chaining is bad news is fair - especially as a proposed permanent installation. However, if you do understand what you're doing and know what's what, then this is not such a bad practice. I often wind up on a temporary basis with a string of 2 pin (with 'plastic earth') wall warts plugged in to a six way distribution block plugged in to a four way long run which itself is powering very low current bits of electronic kit. I fail to see any danger as the earth isn't needed as it's double insulated kit producing low voltage supplies fully floating from earth.

In the past I've worked round this problem by using fused 6A IEC distribution but with 13A plug wall warts you can't do that! Not everything is 12V, so LV distribution doesn't work either.

'Rules' like this can be taken too far and in competent hands for short-term use the dangers are very low. Each case needs to be considered on its merits and risk.

Cheers,

Paul M

[M0FYA Andy]

Originally Posted by rambo1152

An even more important consideration is, if the extension leads are the type on a reel, you must uncoil the reel completely. A coiled up cable can become dangerously hot, at a fraction of its rated current capacity.

I can relate an amusing experience, dating back to the early 70's. I was visiting my brother who was at teacher-training college in York, and was involved with the stage-lighting for a Stefan Grappelli concert. We were up on the balcony where the spot-lights were being supplied from a large cable-drum, most of the rubber-insulated cable was still wound on the drum.....
Part way through the concert, somebody whispered 'something's burning'. The cable on the drum was almost too hot to touch! The choice was risk unwinding the live cable, the insulation of which was now sticky to touch, or plunge the concert into darkness.
We chose to unwind the reel and lay it out along the balcony, and got away with it.
H & S anyone?

Andy

[Dai Corner]

You can buy mains extension leads with up to 12 outlets from reputable suppliers like CPC and RS.
Presumably these are considered safe.

[gramophone1]

I have a 6 way extension, which I planned to daisy chain another 6 way on to it. Cable length will only be half a metre between each extension, as they will sit along side each other. Each extension will be the same manufacturer.

Would this work . . . ?

The reason I don't want to buy an extension block with extra sockets, is because I purposely bought one that was unwired, so I could wire in my own cable, and all of the unwired mains extensions I have come across are maximum of 6 sockets.

[paulsherwin]

In practice it will be fine for low current appliances like solid state hifi separates given the short cable lengths. As has been suggested, the general 'dangerous' advice is to discourage members of the public from doing stupid things.

[Radio Wrangler]

You get distribution panels in rack cabinets with maybe 20 devices being powered. It all comes off one 13A plug with one 13A fuse and everyone is happy. If the total load is comfortably below 13A, It doesn't matter from the normal power consumption how the splitting is arranged. If an RCD is used then earth fault impedance is a lot less critical.

I'd opt for hierarchical branching rather than daisy-chaining because it can give lower resistances. Also, any particularly high power devices can go further up the hierarchy.

David.