Daisy chaining power strips?

[FL630]

I'm sorry but surely it is numbers? What in electronics is beyond the amps volts and resistance?

I appreciate that a 4 socket plug is designed and stamped to deliver the power that 4 devices provide, but what is the difference between a kettle in one of these plugs and another 4-socket strip with 4 low power devices on it?

 

[neodude]

My analogy was accurate... just because your setup hasn't set your house on fire, it doesn't mean that your setup is safe. It's not about adding up numbers and calculating figures, it's about good practice and common sense.

You're not explaining exactly why though? Why EXACTLY is running 2 daisy chained power strips with a total current draw of less than 3 amps so dangerous compared to running the same appliances on one strip?

Yes, I get that there is a (very) slightly increased risk due to introducing another point of failure. But akin to "driving at 130mph"? By the same argument introducing anything between the direct connection between wall and appliance is just as dangerous?

• So using an appliance directly into a wall socket is safe.
• Using 4 low power appliances via a 4-way power-strip is safe
• Using the same 4 low power appliances via 2 daisy chained power-strips - YOU GONNA DIE!
• Using the same 4 low power appliances via 1 power strip plugged into a UPS? Am I still gonna die? Surely there's more points of failure here than the 3rd situation?

Your 10 way strip has all the sockets linked by solid busbars inside the strip. All the interconnections are mechanically protected by the plastic moulding. More importantly, there is a CE label affixed to the socket to tell you that the 10 sockets, in this format, have been tested for mechanical and electrical integrity and that the unit has met the standard. When you start to daisy chain, you are creating connections that as @EVH has pointed out will increase your risk. It's not all about amps and volts. You now have a cable that is strewn from one strip to the other, and it doesn't have the same level of mechanical protection as a busbar encased in a plastic mould. If that cable is tucked under a carpet, then the current carrying capacity of that section of the circuit is now compromised and reduced due to the increased heat. If there is a fray at the stud of one of the plug pins, then the current carrying capacity of the cable has been compromised further. At no point during these fault conditions has the amount of watts you are consuming been increased or decreased, the risk is from the mechanical damage. These set ups can be in use 24/7 month after month, sometimes for years... and that's where deterioration starts to play a part, because the increased heat is starting to erode the insulation resistance properties of the cable and a vicious circle is in full flow.

All of these arguments are valid for just a single power-strip too. What makes daisy-changing so inherently dangerous?

 

[Dirk Diggler]

I'm sorry but surely it is numbers? What in electronics is beyond the amps volts and resistance?

I appreciate that a 4 socket plug is designed and stamped to deliver the power that 4 devices provide, but what is the difference between a kettle in one of these plugs and another 4-socket strip with 4 low power devices on it?

If you had to split a neutral connector by partially fraying a flex and the line conductor remained intact, then the lamp would go out. If you had to make contact with the load side of the neutral, then you'd receive a continuous electric shock that would not blow the fuse or lift the circuit breaker. If you had to measure the current in the circuit during this electric shock, then you would likely see a reading of approximately 0.25A. After a minute, you would probably be dead.

Put that in your calculator.

 

[neodude]

If you had to split a neutral connector by partially fraying a flex and the line conductor remained intact, then the lamp would go out. If you had to make contact with the load side of the neutral, then you'd receive a continuous electric shock that would not blow the fuse or lift the circuit breaker. If you had to measure the current in the circuit during this electric shock, then you would likely see a reading of approximately 0.25A. After a minute, you would probably be dead.

What does any of that mean? lol.

I'm assuming you mean "Neutral Conductor" and "Live Conductor"?

What does any of that have to do with the discussion?

(And actually, in reality, with AC current you would probably be thrown off the conductor before receiving a fatal shock. I've had 3 mains shocks in the past. DC is a different matter)

 

[FL630]

One would hope my desire to play computer games wouldn't end in my death. Having also had several mains electric shocks in my time I do not need a calculator to remind me that they hurt a little.

So are you saying that, hypothetically, a 100% intact, non-frayed and structurally perfect power strip would be safe to daisy chain given that the total power requirement is lower than the requirement of Strip-A? Rather, the risk comes in the more points of failure to cause a fire than the actually electricity part itself?

 

[Swanster]

If you had to split a neutral connector by partially fraying a flex and the line conductor remained intact, then the lamp would go out. If you had to make contact with the load side of the neutral, then you'd receive a continuous electric shock that would not blow the fuse or lift the circuit breaker. If you had to measure the current in the circuit during this electric shock, then you would likely see a reading of approximately 0.25A. After a minute, you would probably be dead.

Whilst I don't disagree that's a possibility, how is that specific to daisy chaining extension leads?
If you had a fraying flex without an extension lead and made contact with the supply side of the line conductor, you'd also get a shock. It also wouldn't be anywhere near enough to pop a 13A fuse, but would be more than enough to kill you in under a minute.
Both cases should still trip an RCD if you have one, not that you should rely on it.
The only way I guess it probably wouldn't trip an RCD is if you came into contact with both side of the broken neutral at once...

 

[Dirk Diggler]

What does any of that mean? lol.

I'm assuming you mean "Neutral Conductor" and "Live Conductor"?

What does any of that have to do with the discussion?

(And actually, in reality, with AC current you would probably be thrown off the conductor before receiving a fatal shock. I've had 3 mains shocks in the past. DC is a different matter)

Neutral conductor and line conductor.

I am making the point that there are situations that numbers don't explain, and your quote in brackets simply proves that. If you had experienced the scenario I described, you would not have been thrown off the AC circuit.

So are you saying that, hypothetically, a 100% intact, non-frayed and structurally perfect power strip would be safe to daisy chain given that the total power requirement is lower than the requirement of Strip-A? Rather, the risk comes in the more points of failure to cause a fire than the actually electricity part itself?

Yes, essentially that's what I'm saying. However, the numbers associated with the electrical come into play when you start to increase the number of outlets e.g. in the case of a 16 way power brick. You don't have to daisy chain them to be at risk, and that's where the common sense comes in e.g. don't plug in 16 kettles (exaggerated example).

 

[neodude]

So, we finally got there eh? In answer to the OP, No, there won't be any issue with you daisy chaining 2 power strips as long as you're not planning on running 3KW heaters with them, and as long as they are in good nick.

 

[Dirk Diggler]

Whilst I don't disagree that's a possibility, how is that specific to daisy chaining extension leads? It's not.
If you had a fraying flex without an extension lead and made contact with the supply side of the line conductor, you'd also get a shock. It also wouldn't be anywhere near enough to pop a 13A fuse, yes it would, it would create a short circuit but would be more than enough to kill you in under a minute.It would last less than a second and probably wouldn't kill you if you were healthy.
Both cases should still trip an RCD if you have one, not that you should rely on it.
The only way I guess it probably wouldn't trip an RCD is if you came into contact with both side of the broken neutral at once... An RCD was not part of the scenario, but yes that would break the circuit (it's why they were invented).

 

[Dirk Diggler]

So, we finally got there eh? In answer to the OP, No, there won't be any issue with you daisy chaining 2 power strips as long as you're not planning on running 3KW heaters with them, and as long as they are in good nick.

Having read the thread, the OP will be well aware that his father was right.

And the conversion took many a tangent due to some of the horrendous advice and anecdotes shared... But the actual answer to the OP is: "Probably".

 

[Swanster]

yes it would, it would create a short circuit

How would that cause a short circuit? The not insignificant resistance of the human body would result in far less current than 13A flowing, even in the worst case of touching line and neutral at the same time, yet still more than enough to potentially kill you.

 

[neodude]

And the conversion took many a tangent due to some of the horrendous advice and anecdotes shared...

...and some overly dramatic scare-mongering.

But the actual answer to the OP is: "No, it'll be fine".

 

[Dirk Diggler]

How would that cause a short circuit? The not insignificant resistance of the human body would result in far less current than 13A flowing, even in the worst case of touching line and neutral at the same time, yet still more than enough to potentially kill you.

Yet another tangent, but hey ho.

If you touch the line conductor anywhere in the circuit then you create a fault path to earth. The amps will go high enough to lift the breaker or fuse.

If you touch a neutral conductor then you won't receive any shock whatsoever as it's 0v.

If you split a neutral and touch the return side you will receive no shock as it's 0v.

If you split a neutral and touch the load side then you'll get one horrendous shock as you'll become part of the circuit and the load current will run through you.

All of the above assumes no RCD.

 

[Swanster]

Yet another tangent, but hey ho.

meh, tangents can be enlightening, and the original question seems to have be answered now anyway.

If you touch the line conductor anywhere in the circuit then you create a fault path to earth. The amps will go high enough to lift the breaker or fuse.

Wikipedia is telling me that the resistance of a human body is generally >= 1k Ohms. To get the >= 13A flowing though the body and blow the fuse, the resistance would need to drop to <= 240/13 = ~18 Ohms... What am I missing here? The fuse isn't going to save you..

 

[Unicorn]

Wikipedia is telling me that the resistance of a human body is generally >= 1k Ohms. To get the >= 13A flowing though the body and blow the fuse, the resistance would need to drop to <= 240/13 = ~18 Ohms... What am I missing here? The fuse isn't going to save you..

A fuse isnt designed to save a human, Its designed to protect the wiring of a circuit only. It should never be relied upon to trip if you were to touch it, this is the job of an RCD

 

[Dirk Diggler]

meh, tangents can be enlightening, and the original question seems to have be answered now anyway.


Wikipedia is telling me that the resistance of a human body is generally >= 1k Ohms. To get the >= 13A flowing though the body and blow the fuse, the resistance would need to drop to <= 240/13 = ~18 Ohms... What am I missing here? The fuse isn't going to save you..

You could touch the contact with your finger and have the heel of your hand on a piece of metal. You would receive burns to your skin due to the current. The resistance you quote wouldn't be relevant as the path would be so short i.e. not traveling through the full body. You wouldn't die because the disconnection time of the circuit breaker is designed to be in the milliseconds.

You could be insulated enough that you didn't receive a shock at all.

There are many permutations of what could happen. I speak from experience not theory. I've had shocks from non RCD protected circuits and I've lived and the circuit breaker tripped. I've had one shock from the split neutral scenario I provided above and again there was no RCD as it was a lighting circuit, I came very close to death because the protective device wouldn't trip. I was unconscious for a short time afterwards but thankfully I wasn't working alone at the time and my work colleague saved me with a swift kick to the stepladder.

RCDs negate all this now, but alas not all domestic installations have them which is in line with the regulations, strangely enough.

 

[Buffman]

As long as you're not using high power devices it won't cause an issue (eg kettles, heaters, etc...)

Im sure all the electrical gurus above are correct that it's bad practice, but if it's for low power PC kit, tv etc it will be fine. My parents have about 30 devices daisy chained of a set of two way sockets in a room (PC and tv gear). You've also got to consider redundancy in the system (ie not all running at once).

I'd say don't under or over think it tbh.

 

[Swanster]

A fuse isnt designed to save a human, Its designed to protect the wiring of a circuit only. It should never be relied upon to trip if you were to touch it, this is the job of an RCD

Well, yes, I agree - but that is exactly my point - if you touch a live circuit the fuse is rather unlikely blow (I didn't mean to suggest it should).

You could touch the contact with your finger and have the heel of your hand on a piece of metal. You would receive burns to your skin due to the current. The resistance you quote wouldn't be relevant as the path would be so short i.e. not traveling through the full body. You wouldn't die because the disconnection time of the circuit breaker is designed to be in the milliseconds.

Ignoring that scenario being quite different to touching the line conductor of a frayed flex for a moment... I totally get that it could give you burns. But I can't find anything that suggests the resistance of the human body gets anywhere even remotely close to the low value required to blow a 13A fuse, let alone trip a 32A circuit breaker.
It sounds like you've been very, very, lucky in the past if a fuse blowing has saved you.

 

[GeX]

Before something goes on fire, it tends to heat up. That's what was happening in your example, and your power meter can only tell you how much power is being drawn... It can't tell you the resistance of the cable or whether it is capable of carrying the current you were putting through it.

Electrical cables should never, ever be hot. If cables are hot, it means they're pulling too much current and the fuse hasn't blown. That's a potential disaster in terms of safety.

I wasn't saying "Yes, do this - it is perfectly safe". More so offering anecdotal words.

It is my understanding, though, that the fuse is there to protect the wiring. The wiring should be rated higher than the fuse, and if there is too much current being drawn (causing the wire to overheat) then the fuse should blow first. In what I was seeing, it was the wire directly from the power meter that was getting slightly warm. Not hot. I understand and agree that they should never get warm, but if the wire was carrying enough current that this was happening then shouldn't the fuse have blown as the wire should be rated higher than the fuse.

I understand your point about daisy changing altering the characteristics. In a nutshell, are you saying that a 4-way extension lead does not mean you have 4 sockets that are rated to take 13A? I appreciate that you can't load each one at 13A, but surely given they could be used to connect a 13A load they should be rated (including the mechanical aspect, busbars) for at least one of them to draw 13A. If you tried to load two at 13A, you'd exceed the safe current carrying capacity of the wire (15A?) and the fuse would blow.

I am looking at an extension lead now, it says "13A 250V a.c BS1363/A. Total load must not exceed 13A." There is no restriction on the individual sockets.

 

[HardwareGeek]

One thing not mentioned so far is quality of the extensions, lots of cheap crap about, if you look at the decent ones they have thicker flex and better sockets that accept and hold the plug better, whereas as the cheap ones either hold the plug too loose which will heat up or you have to force the plug in, seen a lot of cheap ones with broken casing, exposing copper bar inside due to forcing plug in and things like 1 of 4 sockets on the same extension not working, or working but not earthed because the contacts have failed and not contacting the plug correctly

also seen a lot of sockets overloaded with melted / burnt out pins on the plugs and terminals on the socket, plugs melted to the socket etc, kitchens with wm and td sharing 1 2 gang socket etc. also cause switches on the sockets to fail due to heat. this is just from relatively small overloads of 2 x 13a on a 2 gang rated for 20a etc or just old worn sockets not holding the plug securely and causing it to heat up, or loose wire at socket or plug end causing overheating

also 13A fuse will let 19 to 21 A pass forever before blowing, will probably need 100a to blow instantly, check fuse current characteristics for exact numbers, so can have long term overheating causing damage

Also cable is rated to run at 70 degrees which will be too hot to touch but wouldn't be sensible to run it anywhere near the limit

i would say use common sense, buy a good quality extension, buy the correct size rather than daisy chain ideally, don't use more than 2 chained together, don't pull anywhere near the max rating, use for lots of low power stuff only, not high power items, play it safe.