Daisy chaining power strips?

[Dirk Diggler]

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.

The cable will be rated slightly higher than the outlet, so cable 15A and outlet 13A. The cable only maintains that rating and integrity if:

• It is not lenghthened (daisy chain).
• It is not damaged (insulation resistance).
• It is not overloaded (heat degradation).

Whilst the fuse is rated at 13A, this is the maximum current that it will allow without overheating (that would lead to degradation as discussed above). There has to be a tolerance between rated current and the current that will blow the fuse. In the case of a 13A fuse, it will allow around 22A of current before it thinks about rupturing. This is more than the outlet or the cable are rated for, and it's why they'll heat up and degrade over time.

 

[GeX]

OK. TIL; http://www.pat-testing-training.net/articles/fuse-operation-characteristics.php

BS 1362, the British Standard for plug fuses, specifies a maximum power dissipation of one watt when carrying the rated current. The actual current, where a BS 1362 fuse will blow, is about 1.66 times the rated value, so for a 13A fuse this will be 21.6A.

This seems somewhat ridiculous.. how is a 13A fuse meant to protect 15A cable if it will allow 22A indefinitely. Shouldn't a standard socket allow for this heat to dissipated?

I understand that the current carrying capacity of a cable varies depending on how it's installed / clipped / covered but there isn't that much variation in the cable that would be used for extension leads, is there?

If it's 1.5mm cable, what is the difference if there is | socket -> 2m cable -> 8 way -> 7 x 250w loads | vs | socket -> 1m cable -> 4 way -> 3x 250w loads & 1m cable -> 4 way -> 4 x 250w loads ?

 

[Dirk Diggler]

This seems somewhat ridiculous.. how is a 13A fuse meant to protect 15A cable if it will allow 22A indefinitely. Shouldn't a standard socket allow for this heat to dissipated?

Because it's not there to protect it from overload current, that's your job. It's there to ensure that when there's a short circuit it will break the circuit in a quick enough time so that you only need to replace the fuse as opposed to having to replace the cable and apparatus too. A fuse that could break at 13A would be rated at around 8A and that would run constantly hot in a 13A circuit.

To be fair, this has all been covered in previous posts by more than just me. Why can't people accept that's how it is?

 

[GeX]

Because it's not there to protect it from overload current, that's your job. It's there to ensure that when there's a short circuit it will break the circuit in a quick enough time so that you only need to replace the fuse as opposed to having to replace the cable and apparatus too. A fuse that could break at 13A would be rated at around 8A and that would run constantly hot in a 13A circuit.

I didn't realise that that is all the fuse is intended to do, I thought it was to protect the cable from over-current in normal use.

To be fair, this has all been covered in previous posts by more than just me. Why can't people accept that's how it is?

I have issue with 'accepting' things. I want to understand why, and I thank you for replying as I feel like this is making sense now.

Back to the topic of daisy chaining;

If it's 1.5mm cable, what is the difference if there is | socket -> 2m cable -> 8 way -> 7 x 250w loads | vs | socket -> 1m cable -> 4 way -> 3x 250w loads & 1m cable -> 4 way -> 4 x 250w loads ?

The thing I'm getting at is that it's not an issue with daisy chaining, it's an issue with overloading.

 

[Dirk Diggler]

The thing I'm getting at is that it's not an issue with daisy chaining, it's an issue with overloading.

It's been covered by @EVH

You could see one extension fail unsafely which then causes issues with the others. As stated above, you increase the likelihood of a 4-way extension failing safely by 16x, if plugged in to another 4-way. You’re dealing with 2 “devices” each carrying multiple appliances, instead of one device carrying them all.

Typically if your single extension goes pop, that’s it.

 

[GeX]

OK, thanks. Missed that.

Following on from that, assume it's not overloaded or has been damaged - why would a simple extension lead fail?

 

[Sasahara]

String is mostly correct, but going a bit OTT.

I have a chained a high quality surge strip to another high quality 4 gang surge strip. The first strip has 3 devices connected. 1 monitor 50 W, a lamp 15 W and a halogen heater 800 W max(1 bulb is dead ). The chained strip has a TV 150 W max HDR (70-130 W normal), PS4 Pro 200 W max, PS3 and small Blu-ray player. Now while I'd admit I wouldn't recommend this set up, I would still consider it being safe. The chained strip idle load is under 25 W, which is most of the time. And max realistic usage is under 400 W. The total max usage on the main strip plus the 2nd strip would be 1200 W and this would be an usual usage and I would be present if this was the case.

Both strips power leads are extended (1.5 m) not wound as that had potential for heating though short cables like these are not really long enough to be a problem.

This said I'm the only one that has access to this so there is no chance someone is going to plug something else in and overload the circuit.

If the equipment is in good working condition there is no extra risk here than having both strips connected directly to the wall.

My personal limit for a single power strip would be 2.5 kW, I wouldn't be happy pushing much past this. And it would be very odd usage anyway.

2. 13A sockets can be loaded up to 13A. These sockets are designed to withstand 13A, they aren't designed to provide 13A. Let's forget the amps and volts for a second and speak in terms that everyone understands: Money. If you loaded up one single 13A socket with every one of those 13A and run it 24/7, it would cost you roughly £33/month (£400/year) at an average price of £0.20/Kwh. That's just one single plug. The average house has around 20 of these socket outlets, each with 2 gangs that can "give you 13A". That's us now consuming around £1,333/month (£16k/year). No one consumes that amount of electricity in a domestic dwelling, which is why domestic installations aren't designed for that level of consumption.

I think you have messed up the costs here. (I wish you made my electric bills) £0.20 / kWh is a bit high, but even on £0.12 / kWh.
3.120 kW 24/7 would cost you £270 per month (30 days), £3,240 a year. if you had 20 of these running (impossible as your domestic consumer unit wouldn't allow it), it would cost you £64,800 per year. :O

 

[itchy]

Its not a problem I have done it for years and with heavy loads as in 3kw.

Problems occur with bad plug contacts if they arc, which only usually happens under heavy loads.

I have had a few fishy knickers smells over the years and its always down to plugs arcing or low gauge wires being used.

Double adapters and triple adapters are a no go with me, providing you use the correct amp wire and socket you will be fine under low voltage.

I always go for fire resistant cables at 2.5mm and make sure the plug contacts are spot on.

Also make your cables as straight as possible, no curly wire in the corner because its too long as this increases heat and can be dangerous.

 

[Skynet5]

Just don't over load the socket. 13A right? So 13*240 = 3120Watts. So running 4-5 SLI rigs from the same socket aint a good idea