Check for overloaded cables?

[tgd241]

That sets alarm bells ringing!


Yes, but you need to investigate what has been added to that ring, how, and why all the JB's....

There was a method, more common in bungalows, where a ring would be installed in the loft, then a JB added where a socket was required, with a single 2.5mm dropped to each socket. Is this a bungalow?

I dont think the method you decribe has been used originally. This looks more like supplies to extensions and various addons were needed but they didnt want to put in new circuits or redo existing chases.

I was hoping not to have to do a full tracing out but maybe there isn't as much left to do as I thought. The issue is having to lie down with my face full of stinking, decaying insulation wool around the eaves. Are there any shortcut methods using a multimeter that don't require disassembling the terminal blocks on every socket?

 

[Harry Bloomfield]

Are there any shortcut methods using a multimeter that don't require disassembling the terminal blocks on every socket?

No, none.

 

[JohnW2]

Is there a tool that can easily detect overloaded or overheating cables? I want to add 2 or 3 extra sockets in a property, but the existing installation is a nightmare. I just want something I can plug into each socket to give me a reading for peace of mind (or not). Is there, for example, a tool that draws the rated current and checks for an acceptable voltage drop over time? For example by drawing the maximum rated current and checking for an acceptable voltage drop over a certain time?

It is not clear (at least, not to me!) what your concern is.

Provided only that the circuit was installed correctly, there should be no risk of the cable becoming overloaded or 'overheating'. Specifically, if the size of the cable (and how it is installed - e.g. whether 'buried in thermal installation') is appropriate for the rating of the MCB protecting it, there is no risk of the cable being o'overloaded' to a dangerous extent, and that would remain true no matter how many additional sockets you added (provided they were added correctly').

Virtually any sockets circuits will have far more 13A outlets for it to be theoretically possible to 'plug in' loads which, between them, represent far too great a load (current) for the cable - but if that situation arose, the MCB would trip before any harm came to the cable. Hence, as above, adding more sockets would not change anything.

Asfar as the cable (and risk of it being overloaded) is concerned, total voltage drop is not really relevant - it's the 'voltage drop per metre of cable' (which is directly related to current) that matters, regardless of the length of cable and hence the magnitude of the voltage drop. If a cable of a certain size 1 metre long is safe when carrying a certain current, then the same cable would also be safe (for the same current) if it were 100 metres long.

If you had reason to doubt that the circuit was originally designed/installed correctly (particularly in relation to cable size), then there could be issues (particularly those relating to 'fault protection') other than 'overloading' to consider - but you would then really need an electrician with the appropriate knowledge and test kit to investigate.

Kind Regards, John

 

[martygturner]

I was just going to point out that a ring circuit is already protected from overload by its maximum demand being derated from the maximum performance of the cable which for twin and earth 2.5mm is 25 amps single and 45 amps ring. So the 32 Mcb will trip long before the cable melts. Voltage drop in 150m of twin and earth is 0.49% pretty negligible.

What can cause ia voltage drop is loose connections in the sockets. If you are going to add sockets it may be a worthwhile to ensure that all your existing sockets are sound, the wires are tight and just don't drop out, remember on a Eicr 10% sample of sockets is about it. Tools needed a screwdriver and isolating the circuit safely.

If you are going to DIY, a plug in socket tester in a must - £10ish, which will tell you if all the sockets are wired round the right way have a earth and are definitely off before you start grabbing wires.

 

[JohnW2]

I was just going to point out that a ring circuit is already protected from overload by its maximum demand being derated from the maximum performance of the cable which for twin and earth 2.5mm is 25 amps single and 45 amps ring.

I'm not sure what you are trying to say here.

The current-carrying-capacity of Method C 2.5 mm² T+E is 27A.

 

[JohnW2]

Voltage drop in 150m of twin and earth is 0.49% pretty negligible.

I'm afraid that I understand even less what you are trying to say here.

150m of 2.5 mm² T+E would have a VD of 86.4 V (37.6%) with 32A or 54 V (23.5%) with 20A.

Even 150m of 2 x 2.5 mm² cables in parallel (i.e. 5 mm² overall) would have a VD of 27 V (11.7%) with just 20A.

 

[LaurenFan5]

There is no simple “plugged into the outlet and checked the security of the wiring” device. There are only load meters (wattmeters) that show voltage, current and power, but they do not guarantee that the wiring does not overheat in the wall. For a real test, you need professional devices or an electrician who will test the load and resistance of the line

 

[JohnW2]

There is no simple “plugged into the outlet and checked the security of the wiring” device. There are only load meters (wattmeters) that show voltage, current and power, but they do not guarantee that the wiring does not overheat in the wall. For a real test, you need professional devices or an electrician who will test the load and resistance of the line

The "resistance of the line" is only relevant in as much as, together with knowledge of the length of the cable, it is an indicator of the 'size' (cross-sectional area) of the cable.

As I've written, all that matters to avoid the risk of 'overheating' is that the size (cross-sectional area) of the cable, and the method by which it is installed (e.g. whether or not within thermal insulation) are appropriate to the rating of the overcurrent device (MCB, RCBO or fuse) in the CU which is protecting it.

 

[securespark]

IMHO, the OP should get an EICR carried out by a reputable electrician and take things from there.

To say

A full rewire isnt gonna happen .

is flippant. If the EICR says the property is dangerously wired and a full rewire is prudent, that is what you ought to do, for your safety and that of the people who share your house, at the very least.

 

[JohnW2]

IMHO, the OP should get an EICR carried out by a reputable electrician and take things from there.

That's always reasonable advice if there are any concerns (or merely if it's a very long time since the installation was last inspected). However, although he/she described the electrical installation as 'a nightmare', I don't think the OP has yet told us anything specific to indicate that there is any particularlyurgent need for an EICR.

Let's face it, as far as I can see the reason the OP raised his/her questions is because of a desire to add two sockets, not (as far as I can make out) that there are currently any apparent 'problems' with the installation.

 

[JohnW2]

The voltage at the CU should be known, let's say 230V. A diagnostic tool plugged into a socket should be capable of drawing a known, fixed current and measuring the voltage at the socket, giving a voltage drop and resistance of the cables.

Indeed.

If you also give it an estimate of the cable length, this should tell you whether the resistance is within acceptable limits, no?

As I've said, the voltage drop together with length and current will enable you to determine the size (cross-sectional area) of the cable) and thus whether it is adequately protected (from overload/overheating) by the MCB protecting it. It is not 'resistance' that has 'acceptable limits'

Furthermore, the tool should be able to detect if the resistance is constant over time , or increases in a manner consistent with and overheating cable somewhere.

At a given temperature, resistance of the conductors of the cable will remain constant, regardless of what current is flowing through them. However, any current will result in at least some rising of temperature, and that will, in turn, result in a (fairly small) increase in resistance.

So let's say you plug this tool in an every socket, and have it draw as close as possible to the rated current of the circuit at every socket.....

As I've said, with most sockets circuits, if you plugged a load into every socket outlet you would seriously overload the circuit (and cable) and cause the MCB to trip. A sockets circuit would commonly have at least 8 double sockets (hence 16 13A socket outlets) - that's a potential load of 512 A, far, far too much to be 'allowed' to flow for very long by a 32A MCB (which would trip within an hour with, much faster with higher currents and within milliseconds with 160A)

If you're not getting a rising resistance or as long as the resistance plateaus at some acceptable value, all is well in theory?

As above, the resistance will rise as little as the cable warms up but, for any particular constant current, will eventually reach a 'plateau' when thermal equilibrium is achieved. The resistance of a copper conductor will increase by about 0.39% for each degree C rise in temp. Hence if the temperature rose from an ambient temp of, say 20°C to the maximum permissible work temp of the cable (typically 70°C), the resistance would increase by about 19.5%. However, this is not a way of investigating anything, not the least because that temperature rise is merely an indication/measure of the amount of current flowing (which will be known and/or can be measured).

I still don't really understand what makes you suspect/fear that there might be a risk of 'overheating' in your installation.