Multiple extension leads on plug sockets

sonysean

Member
Having a bit of knowledge and common sense when it comes to electronics and the fact I've had my plug sockets arranged like this for a very long time I'm not really sure why now I've decided to ask what others think in the regards to it being 'safe', but here goes.

I'm quite limited for wall sockets unfortunately so I've got 2 gang plug on the wall with things plugged in as follows:

Wall plug 1 -> 2 way block adapter ->
1. 8 gang surge extension lead -> TV, receiver, blu-ray player, PS3, PS4, Sky Q, Harmony hub, Echo dot.
2. 6 gang extension lead -> LED light, subwoofer, switched 4 way lead (fish tank pump x2, LED light, heater)

Wall plug 2 -> 3 way adapter ->
1. Harmony remote charger
2. Smart extension lead (Lava lamp, LED light)
3. 2 way extension lead (LED lamps x2, Infrared hub)

It sounds like a lot I guess, but the majority of these devices are very low power, with the highest being the TV and receiver (200w ish and 400w ish?).

I guess I'm just curious as to what others think to my arrangement, and how others deal with a lot of devices with very little wall sockets.
 

sonysean

Member
Add more wall sockets?

I don't feel confident enough to DIY my own and it seems unnecessary to pay for it to be done as I don't personally think there is anything wrong with the way I have them plugged in now.
 

mushii

Distinguished Member
Its not just about how much current that devices draw in normal state, its about how they behave in fault mode and the knock on effect to other devices. When these devices go for their CE marking or whatever conformity testing they have, they will test for fault conditions based on a single device in a single socket, not potentially 14 devices off one socket (which IMHO is way too many). The 8 gang is the maximum you should have off any one socket, adding another 6 gang off a 2 way is just way too much. I think that if you showed that to any electrician or safety professional they would agree with me. I actually think that socket is a potential fire risk. In fact I wouldn't allow any my family to sleep in house where that kind of wiring arrangement existed.
 

Frederico21

Standard Member
Pretty sure it does only depend on current draw, not sure what fault mode has to do with anything.
If it does feel free to explain better.

Are you saying they could all short at the same time?
All the devices above draw virtually nothing., maybe a kW if most were on at the same time.
Presumably an rcd would click in as soon as a short happened.
 

outoftheknow

Moderator
Pretty sure it does only depend on current draw, not sure what fault mode has to do with anything.
If it does feel free to explain better.

Are you saying they could all short at the same time?
All the devices above draw virtually nothing., maybe a kW if most were on at the same time.
Presumably an rcd would click in as soon as a short happened.
Presumably an airbag will deploy if I crash.....

Seriously though electricity is dangerous stuff. The fact the OP said they know what they are doing isn’t right is a clue. There Is no other answer than it isn’t safe. No need for quotes around safe.

Sure safety websites back up the theory that as long as the maximum current isn’t exceeded all is well.


it’s your house though OP so no worries from my point of view :)
 

sonysean

Member
I’m very aware electricity is dangerous stuff and I don’t recall saying “I know what I’m doing isn’t right”.

I have common sense and some knowledge surrounding electrics and would never overload a socket.

I’m aware it “sounds bad” with the amount plugged in to the two sockets I mention but if you look at the power those devices are drawing, it should be completely fine and nothing to be concerned about.

TV - 200w
Receiver - 400w
Blu-ray player - 50w
PS3 Slim - 100w
PS4 - 150w
Sky Q - 20w
Harmony Hub - 10w
Echo Dot - 10w
LED TV Light - 15w
Subwoofer - 50w
Fish tank pump x2 - 10w
Fish tank heater - 100w
Fish tank light - 10w

So a total of about 1125watts which is well below the maximum rated power a socket will allow, and that’s with me overcompensating some of those and that’s if they were all on at the same time.
 

mushii

Distinguished Member
And in failure mode when one of those cheap chinese PSUs blows its capacitors, shorts the circuit board (which has no fuse protection) and suddenly pulls down 3kw then all of the other other chinese PSUs and blows that and you get a cascaded effect of non fuse protected devices suddenly pulling waaay more than 1.1kw becuase you have simultaneous or cascaded failure, then something catches fire..... then your 13amp fuse blows.

There is a reason this type of arrangement is not recommended. You have to look at the Failure Mode Analysis to understand what may occur. Not just - 14 devices aren't pulling enough current to overload it.
If I found this arrangements on one of my factories you'd be looking for alternative employment.
 

sonysean

Member
And in failure mode when one of those cheap chinese PSUs blows its capacitors, shorts the circuit board (which has no fuse protection) and suddenly pulls down 3kw then all of the other other chinese PSUs and blows that and you get a cascaded effect of non fuse protected devices suddenly pulling waaay more than 1.1kw becuase you have simultaneous or cascaded failure, then something catches fire..... then your 13amp fuse blows.

There is a reason this type of arrangement is not recommended. You have to look at the Failure Mode Analysis to understand what may occur. Not just - 14 devices aren't pulling enough current to overload it.
If I found this arrangements on one of my factories you'd be looking for alternative employment.

Which of my devices contains a "cheap chinese PSU with no fuse protection" that's likely to cause something like that?

With things like this, isn't it possible for things to "blow" and/or cause fires even without as many devices as this?
To be 100% safe from any electric related fires you'd be better off switching off your entire mains circuit whenever you leave your home, switching everything off such as your fridge freezer, standby items as well as everything else, but I doubt you or many people do that.

I can't imagine that I would have all those things with me let alone plugged in if I was at your factory 😊
 

mushii

Distinguished Member
Evidently you are happy with your arrangement, that is fine. As a H&S manager for 14 Aerospace / Space / Military sites, I see things a little differently. I have seen the consequences of this kind of 'mis adventure' and also do a lot of FMA studies and incident investigations. My specialism is high risk health and safety, ATEX / DSEAR / Explosives. I have consulted world wide for explosives / military / high risk manufacture and am certified as Machinery Safety Expert amongst other things.
You have the value of my expertise and experience. If you choose to ignore it, that is your funeral (maybe literally).
 

sonysean

Member
Evidently you are happy with your arrangement, that is fine. As a H&S manager for 14 Aerospace / Space / Military sites, I see things a little differently. I have seen the consequences of this kind of 'mis adventure' and also do a lot of FMA studies and incident investigations. My specialism is high risk health and safety, ATEX / DSEAR / Explosives. I have consulted world wide for explosives / military / high risk manufacture and am certified as Machinery Safety Expert amongst other things.
You have the value of my expertise and experience. If you choose to ignore it, that is your funeral (maybe literally).

I mainly posted here to get others opinions or what others do when they have a limited socket arrangement, so I appreciate your guidance but no I don’t personally find a problem with how I have things connected.

I don’t see what those things you’ve mentioned have to do with plugging domestic electrical devices in to a house mains socket.

You have said yourself I haven’t overloaded anything, and then have gone on further about them ‘blowing up’ etc but that could essentially happen with any set up.
For example, I could have a dodgy fridge freezer plugged in to the mains by itself, it could blow, go wrong and catch fire etc.

But, providing you have a decent enough RCD which kicks in to prevent things like that from happening, and you’re not overloading sockets or using cheap dodgy plugs/electronics, you should be okay as far as I can see.
 

Nivek TT

Distinguished Member
If you have an RCD and a 13 amp fuse in the plug of the multi adapters, which you almost certainly do, I reckon you're fine.

As you said, everything is low power. Just avoid using your hair straighteners and your kettle off the same multi adapter at the same time. Worst thing that'll happen is you blow that 13 amp fuse and lose power to everything in that multi adapter. The rest of your household wouldn't even notice.
 

ian34g

Active Member
As long as you haven't changed the 13A fuses in the plugs for nails you can't overload the socket as the maximum is 13A no matter how many items you have plugged in.
That said as an electrical installation inspector I hate to see multiways plugged into more multiways and would always recommend extra sockets be installed, wouldn't cost much to add sockets next to existing sockets and these days you can get good quality built in usb chargers.
Electrically the weak point is at any connection and the more you have the higher the chance of arcing at those connections and possible fire.
Multiways and blocks are built to a cost and rarely of great quality.
 

funinacup

Active Member
I thought it was pretty well known that fuses don't blow at their rated current. They're designed to let that amount of current pass through (13amps in this case) and don't automatically blow if that current increases to 14amps. There's a huge margin where the plug and wire etc can be heating up to dangerous levels.

 

ian34g

Active Member
Not really that simple, the cable rated for 13A can take more than 13A before melting the plug top itself can take more than 13A the 13A socket can take more than 13A. As long as you dont exceed the rating its fine. as in dont fit a 20A fuse to the plug.
Its arcing thats the main problem in generating heat which is the next big safety push with arc fault devices. Had these been mainstream in use they would probably have stopped the Grenfold fire from occuring. But these are very new and very expensive at the moment.
 

outoftheknow

Moderator
Having a bit of knowledge and common sense when it comes to electronics and the fact I've had my plug sockets arranged like this for a very long time I'm not really sure why now I've decided to ask what others think in the regards to it being 'safe', but here goes.
I read that as you knowing what the answer(s) were. Either “your right and fine carry on”, or “it’s unsafe”.

IMHO it is a pointless thread in these forums since it isn’t seeking an answer to anything that you dont already know. Or at least you aren’t going to do much except argue against any post that states the fact the practice is unsafe - because you have common sense when it comes to electronics and have done this for a long time.

It is unsafe if like some of us have stated. It is fine as you have stated you are happy with it. It’s your house.

(Edit - you did say you posted to find out what others do with limited sockets - that wasn’t in the OP but the answer was in what I linked - have more sockets installed. That’s what I do and have done. Until then limit each socket to one decent quality extension board with overload protection and RCD and no double or worse blocks)

There forums aren’t usually for affirmation of an unsafe practice. You have that now anyway from others of the same mind. There are no other points of discussion that add to the thread so I am out of here.
 
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noiseboy72

Distinguished Member
Running multiple devices off one extension lead is very common and I can guarantee it is being done on virtually every military, commercial and business site. Have a look in the comms room or server rack and you will find a multi-way power block (extension lead) most probably connected to either a fused spur or 13A plug into the wall! This is not inherently dangerous. These: https://cpc.farnell.com/lms-data/pdu-8ws-v-sp-1u/8-way-surge-pro-13a-pdu-vert/dp/EN84054?st=Single pole single throw are very common.

The danger lies where spare cable is poorly managed and creates a hazard due to being coiled or crammed into too small a space. It's very bad practice to cascade mains blocks. Much better to buy a couple which have enough sockets so you don't need to do so, cut cables to the correct length and re-terminate to remove excess cable and fit the lowest rated fuse you can get away with without nuisance blowing.

Probably worth dispelling the myth about how RCDs will protect the home against all faults. Put simply they won't - and cascading a local device with the one no doubt fitted to the fuse board is of little benefit either. RCDs and RCBOs will only trip if there is an earth fault, not minor overload. A fire or other heating event can carry on quite happily without the trip interrupting the supply until it's far too late. Don't forget that an MCB or RCBO will have an instantaneous trip value of maybe 10x the continuous current and an overload rating of many minutes for a 2x overload.

In short, remove your cascaded extension leads, bin any solid adapters - they have a habit of coming slightly adrift and creating high resistance hot spots and re-plan your electrical connections to minimise risk from fire due to overheating.
 

ian34g

Active Member
Just a slight correction, a RCBO will trip on overload as well as earth fault.
A RCD has no overcurrent protection.
 

noiseboy72

Distinguished Member
Just a slight correction, a RCBO will trip on overload as well as earth fault.
A RCD has no overcurrent protection.
Only on a gross overload will it trip quickly. A 16A RCBO will pass more than 32A for about 10 minutes before tripping and that's quite long enough to set the house on fire.

Never rely on trips to protect against heating events. This needs to be managed through good cable discipline.
 

ian34g

Active Member
Not arguing, just correcting the no overload on a rcbo quote.
It will trip as any mcb of the same rating and trip curve.
And for the most thats good enough, a circuit on a 16A protective device "should" have been designed correctly and have conductor sizes rated to take the time/trip/current characteristics of the circuit.
As you say its the poor connections that get hot through arcing and generate enough heat to cause fires.
A 2.5mm conductor of a ring with a steady 32A load will only be warm to touch and nowhere near hot enough for a fire, a bad joint on that circuit will start welding.
 
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ufo550

Well-known Member
Only on a gross overload will it trip quickly. A 16A RCBO will pass more than 32A for about 10 minutes before tripping and that's quite long enough to set the house on fire.

Never rely on trips to protect against heating events. This needs to be managed through good cable discipline.
I know this is a bit old now, but if your premise was correct, we would be all stuffed, fires all over the place.

Type B MCB’s (for example) will typically trip between 3-5 times their full load current. So the 16A RCBO would trip on overload between 48 - 80A, in milliseconds dependant on the supply details.

In your scenario the installation should be designed to allow for such overloads, without even causing damage to the cable, let alone causing a fire. The case of multiple extension leads is reliant on the 13A fuse in the initial plug. Haven’t to hand the trip curve for that. The fuse in the plug is designed to protect the flex of the appliances, not the final circuit.
 

noiseboy72

Distinguished Member
Yes, apologies, I was thinking of fuses rather than MCBs in terms of trip time, but you are still looking at 1-2 minutes before they will trip on a 2x overload.

I don't disagree with what you say, but more people die from electrical fires than from electrocution. No doubt this is down to the widespread use of RCDs, but these will not protect from overload. The common misconception is that an RCD will protect from all faults.

Cascading extension leads is never a good idea as you are potentially significantly lengthening the circuit, thus reducing the effectiveness of the circuit protection, possibly with coils of unused cable that will form a nice little heating inductor and increasing the number of joins and connectors - which are another source of failure and heating events.

Perhaps the images below illustrate the point. These came from an RAF health and safety manager and presented as examples of near misses he had come across. The cable drum had the correct 13A fuse fitted and was plugged in a 32A radial. Neither protection triggered before the drum caught fire...

1591203071644.png

1591203090801.png
 

ufo550

Well-known Member
Your second pic, is where old adaptors used could overload the socket outlet, later ones did have a BS1362 fuse in them, but adaptors like that aren't good. In the OP's case, connecting trailing lead to trailing lead will obviously not overload the socket outlet, because the initial one will have the same fuse in it. Multiple connected trailing leads, is not a good thing to have, just because of all those flexes present a trip hazard, and excessive amounts of flex that could be subject to mechanical damage.

With your first pic; a cable real will have two operational ratings, one for coiled, the other uncoiled. Some even have a thermal cut, if the reel overheats during use (although I'm not sure how effective that is). However there's no help for some who plug in a high load appliance, into uncoiled cable reel, and use it for an extended time, and not expect it to melt (I'm surprised something didn't trip eventually, looks like some dead shorts going on there?).

But thats not what the OP is suggesting.
 

noiseboy72

Distinguished Member
Yep, I have no argument that a properly fused extension lead will protect those downstream - particularly if the leads are kept short. From what I remember from the presentation, a caterer was using this "magic" extension lead to run 2 x 10A water boilers at the same time. He found if he used a short lead, the fuse would blow after a few minutes, but not with this cable drum! What was happening was that the length of cable was enough resistance to reduce the current below that at which the fuse would blow, so the cable just got hotter and hotter. This was still operating when he got found out by the smoke coming up from under the table cloth...

The other issue with the solid adapters is plugs not fully inserted. Not a major safety issue with shrouded pins, but the pins could arc or overheat if there's heavy current draw due to the reduced contact surface area.

If you read my first post, I see no issue with properly managed extension leads. It's all about designing the installation correctly in the first place and not allowing coils of cable or solid adapters. I use a pair of Leisgang 8 way extension leads for my HT setup, with shorter mains cables where possible. This is perfectly safe, well protected and neat.
 

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