4mm radial from 2.5mm ring on 32A?

[Jonspark]

Go easy I’m new to this but.. I’ve just come across a 4mm radial (garage) being fed from downstairs 32A MCB ring. Trying to locate the connection but question is does this comply with BS7671? I can’t tell if it’s on a 13A FS or not at the moment.

 

[Spoon]

Go easy I’m new to this but.. I’ve just come across a 4mm radial (garage) being fed from downstairs 32A MCB ring. Trying to locate the connection but question is does this comply with BS7671? I can’t tell if it’s on a 13A FS or not at the moment.

Welcome to the forum mate.
How many sockets are wired to the 4mm? If just 1 then you could class it as a spur.
If there was a 13A FS then why the 4mm? 1.5mm would do, depending on the length...
[automerge]1590366525[/automerge]
@Jonspark Jusr for reference mate, look at Appendix 15 of the BBB (Big Blue Book) page 505.

 

[Jonspark]

Thanks Spoon, I did think that was the case just can’t located the connection at this stage. It has 4 double sockets supplying basic equipment such as fridge etc. I guess 1.5mm would have been ok. I’ve heard the term “lollop circuit” used before but this would usually be the other way round i.e 4mm to 2.5. Next step find connection and if not in a FCU then either 1. Put one in or 2. Run 4mm back to CU on 20A OCPD.

 

[Dustydazzler]

If I even find 4mm additions running on a original 32a 2.5 ring circuit my usually feeling is it’s a non-fused spur off a spur of a spur etc

(I also don’t really like 1.5 feeding 13a sockets Just my opinion)

 

[Spoon]

Thanks Spoon, I did think that was the case just can’t located the connection at this stage. It has 4 double sockets supplying basic equipment such as fridge etc. I guess 1.5mm would have been ok. I’ve heard the term “lollop circuit” used before but this would usually be the other way round i.e 4mm to 2.5. Next step find connection and if not in a FCU then either 1. Put one in or 2. Run 4mm back to CU on 20A OCPD.

There are a lot more knowledgeable people on here regarding the domestic side.
Hopefully someone will confirm what I have said above..... or say I'm talking rubbish..

I would have thought that if there was a 13A fused spur feeding the 4 appliances then this would keep blowing... Depending on what appliances they are and when used.

(I also don’t really like 1.5 feeding 13a sockets Just my opinion)

I know what you mean, but it's there in Appendix 15.

 

[telectrix]

if it's fused at 13A then 1.5mm is adequate, (dependent on installation method, and not derated below 13A).

 

[happysteve]

Thanks Spoon, I did think that was the case just can’t located the connection at this stage. It has 4 double sockets supplying basic equipment such as fridge etc. I guess 1.5mm would have been ok. I’ve heard the term “lollop circuit” used before but this would usually be the other way round i.e 4mm to 2.5.

Sounds like you've got the long and short of the situation. The following is just a technical note.

The arrangement you describe in the house is fundamentally different from a lollipop circuit,* which is: 32A OCPD --> 4mm (or 6mm) --> 2.5mm ring - in terms of safety and risk of overload.

If it's OCPD --> 4mm --> 2.5mm ring then provided the usual rules for RFC are adhered to, such as spreading the loads around etc, it will not be overloaded. Other than potential confusion to future people carrying out inspection and testing - which can be mitigated by documentation, labelling, and making sure the top of the lollipop stick/the start of the ring is accessible for inspection and testing, it is no more dangerous than running the two ends of the ring back to the breaker/fuse.

However, the situation you describe - 32A OCPD --> 2.5mm ring --> 4mm spur --> several sockets - could lead to overloading, depending on where on the ring the 4mm spur is taken from. If it's on the middle of the ring (roughly equal resistances from the spur point back to the board) then no problem: the maximum current (32A) will be fine on the 4mm, and be split more or less equally down both legs of the 2.5mm ring. But if the 4mm spur is close to one end of the ring (i.e. relatively close to the DB), then the majority of the current will go down the short leg, overloading one leg of the 2.5mm ring.

While at the moment, and usually, there's not much draw on the sockets in the garage, you can't predict what might happen in the future. Perhaps one day somone will want a lot of heaters on in the garage (e.g. to help paint or varnish dry).

Next step find connection and if not in a FCU then either 1. Put one in or 2. Run 4mm back to CU on 20A OCPD.

Good man


* "Lollipop circuit" is not, as we all know, any sort of official or technical term, and as such some people frown on it. But we know what it means, and sometimes it's useful to use phrases that are not official and technical, as long as people can agree what they mean and understand them.

 

[Jonspark]

Thanks all. Only low usage in garage/mancave literally a fridge and phone charging however I guess it could be used for garden tools. Have to take another look this week and see what I find. There is another single socket on a 20A MCB near the CU so might just run some new 4mm back to this breaker.

 

[Pretty Mouth]

However, the situation you describe - 32A OCPD --> 2.5mm ring --> 4mm spur --> several sockets - could lead to overloading, depending on where on the ring the 4mm spur is taken from. If it's on the middle of the ring (roughly equal resistances from the spur point back to the board) then no problem: the maximum current (32A) will be fine on the 4mm, and be split more or less equally down both legs of the 2.5mm ring. But if the 4mm spur is close to one end of the ring (i.e. relatively close to the DB), then the majority of the current will go down the short leg, overloading one leg of the 2.5mm ring.

Interesting discussion. I have wondered whether this arrangement could be safe or not. A couple of thoughts:

A double socket spurred from a double socket on a ring (in the usual accepted way, 2.5mm) could, theoretically, overload the ring at the point it is spurred from if both double sockets were heavily loaded. Granted it is more likely to reach overload in the arrangement you describe, but still possible.

Also, there's nothing I'm aware of to stop you having 2 spurs from the same point on the ring, ie a double socket on the ring, with 2 separate spurs from its terminals leading to double sockets. Now we have the load of 3 doubles all at the same point of the ring, again potentially overloading that point.

With the above in mind, is multiple spurs on 4mm from one point of the ring any worse?

 

[Spoon]

I love these discussions... It's great to learn stuff.

 

[Simon47]

As above, it's non-compliant but also may not be anything to worry about. IIRC, as long as any point loads are at least 1/4 of the ring length away from the CU then it's impossible to overload the shorter leg of the ring.
And lets face it, there's nothing really to stop there being several large loads on sockets close to one end of the ring - depending on the layout of the property, e.g. if the natural layout puts the kitchen right at one end of the ring.