30A terminal blocks on 32A circuut

[LappyGB]

Just wondering whether 30A terminal blocks are normally used on a sockets ring main with a 32A breaker for connecting individual cables. I know the terminal blocks don't meet the amperage of the breaker but my understanding is that 2.5mm cable is only rated to 27A anyway?

I'm assuming that if you doubled up the cable (e.g. temporarily connecting both sides of the ring together when removing a socket) you'd need to cover the full 32A with a higher rated connector?

 

[blup]

Both sides of the ring are connected, it’s a ring

 

[sparkwright]

30 amp blocks acceptable on a ring wired in 2.5mm2 protected by a 32 amp breaker.#

If anything, the terminals can be quite big to get just two 2.5mm2 wires into - so make sure you get a good connection.
I mention this because some blocks are so badly designed the thin wires can fall between the screw and the side of the terminal hole, and so can be loose.

 

[LappyGB]

Cheers for that, thought it might be the case, seemed odd that only 30A are widely available when 32A breakers are usually used.

 

[Murdochcat]

Use wagos

 

[flameport]

seemed odd that only 30A are widely available

Leftovers from decades ago when 30A fuses were common and people thought it was appropriate to conceal round brown junction boxes everywhere.

 

[BS3036]

Given that the cable in a ring final is only required to carry 20A, it is not clear why a connection in that cable should be required to carry more than that.

 

[Harry Bloomfield]

Cheers for that, thought it might be the case, seemed odd that only 30A are widely available when 32A breakers are usually used.

The original fuse wire size, for a ring circuit, was rated 30amps. MCB's came along later, rated 30amps, then 32amps - but MCB's offer might tighter protection than fuse wires. Hence 30amp joint boxes are fine for this use.

Connectors, and joint boxes are only current rated anyway, as a guide, to what size conductors can be joined by them. The current carried by the actual terminals, should be minimised as much as possible, by inserting wires side by side in a connector, or if the meet from opposite ends, so the cross inside the connector.

 

[SUNRAY]

If anything, the terminals can be quite big to get just two 2.5mm2 wires into - so make sure you get a good connection.
I mention this because some blocks are so badly designed the thin wires can fall between the screw and the side of the terminal hole, and so can be loose.

And for that reason I have some sympathy with a sparks who will use 20A choc bloc with both 2.5mm² to be long enough to be clamped by both screws

 

[Harry Bloomfield]

And for that reason I have some sympathy with a sparks who will use 20A choc bloc with both 2.5mm² to be long enough to be clamped by both screws

Some modern choc blocks, use plated steel, so always better to use the screws to clamp, rather than have the block/screws carry current - hence my suggestion to ensure where possible, that the conductors overlap/cross in the terminal/ good copper to copper contact. Older choc blocks used to be decent brass, and brass screws.

 

[JohnW2]

Given that the cable in a ring final is only required to carry 20A, it is not clear why a connection in that cable should be required to carry more than that.

Interesting suggestion.

However, I don't think that, as a generalisation, the CCC of a cable can be taken to dictate the required 'rating' of connectors in that cable. For example, a 1.5mm cable in a lighting circuit (I know! may well have a CCC (Method C) of 20A, but I don't think that could be taken to mean that any connectors in tat cable had to be 'rated' for at least 20A.

In practice, it's really the In of the OPD, not the CCC of the cable, which dictated the 'design currents' (for connectors or anything else).

 

[JohnW2]

Some modern choc blocks, use plated steel, so always better to use the screws to clamp, rather than have the block/screws carry current - hence my suggestion to ensure where possible, that the conductors overlap/cross in the terminal/ good copper to copper contact. Older choc blocks used to be decent brass, and brass screws.

Agreed - and that, of course, was part of the thinking of yesteryear that multiple conductors should be twisted together before termination in a screwed terminal.

 

[BS3036]

What nonsense!

I don't think that, as a generalisation, the CCC of a cable can be taken to dictate the required 'rating' of connectors in that cable.

I didn't say that at all. I was talking about a very specific case of the cable in a ring final. This is the only situation where the cable rating and the over-current protection rating are different.

For example, a 1.5mm cable in a lighting circuit (I know! may well have a CCC (Method C) of 20A, but I don't think that could be taken to mean that any connectors in tat(sic) cable had to be 'rated' for at least 20A.

A totally specious argument, with no relation to my suggestion, particularly because it is not a ring final.

In practice, it's really the In of the OPD, not the CCC of the cable, which dictated the 'design currents' (for connectors or anything else).

Which is, of course, nonsense in the case of the ring final.

I guess you are proposing that it is OK for the cable to melt as long as the connector stays intact.

 

[JohnW2]

What nonsense!

You are obviously entitled to that opinion but, needless to say, I would not agree. I did say that your suggestion was interesting.

I didn't say that at all.....

You didn't, but ....

I was talking about a very specific case of the cable in a ring final. This is the only situation where the cable rating and the over-current protection rating are different.

... the only situation in which the cable rating and OPD rating are different in that direction. As I illustrated there are very common situations in which the difference is much more dramatic in the other situation - such as my example of the common situation of a cable with a CCC of 20A being protected by by a 6A OPD.

Which is, of course, nonsense in the case of the ring final.

As I wrote, an interesting (and arguable) suggestion. However, whilst it may be 'nonsense' in terms of design, that may not be true in terms of usage (over which the designer has no control in the case of a sockets circuit). Provided only that there are sufficient socket outlets sufficiently close to one end of the ring, a user may cause more than 20A to flow in the short leg of a 32A ring final. That is an unavoidable 'feature' of the ring final as allowed by BS7671.

I guess you are proposing that it is OK for the cable to melt as long as the connector stays intact.

Not at all. The connector has no bearing on the theoretical possibility of any of the cable becoming overloaded, and (in the situation we are discussing) no connector is ever going to come to any harm as a result of the current flowing between the conductors 'joined' in it.

As has been suggested by others, this whole discussion about the 'current rating of terminals/connectors' is really pretty moot, since it is (at least, in my opinion) essentially plain nonsense. All that matters is that the physical capacity of the terminals is appropriate for the size of conductors, since the vast majority of current will go directly through the contact between conductors, with very little actually going through the material of the terminal.

In fact, my personal view is that the most important thing is not to use a connector with terminals which have 'too high' a 'current rating', since such terminals are likely to have too large a physical conductor capacity, which is the situation in which contact between the conductors may be less than ideal.

 

[BS3036]

Provided only that there are sufficient socket outlets sufficiently close to one end of the ring, a user may cause more than 20A to flow in the short leg of a 32A ring final. That is an unavoidable 'feature' of the ring final as allowed by BS7671.

This is the only place in your complete word salad that you even attempt to respond logically. Once again you are saying that overloading the cable is acceptable, but not overloading the connector. How can you justify this?

A corollary of your position is that, if you had to replace a section of the ring cable, it would have to be with 4mm² cable.