Difference between Merlin Gerin MCB “C60HB” and “C60H” and should they all be the same.

[SFK]

All, I have a Merlin Gerin distribution board in my garage.

Some 12 years ago I believe that the distribution board was set up as three phase as the then owner of my house had a small tool shop in the 5m x 10m garage. And I believe 10 years ago the three phase was reduced to one phase and 6 MCBs put in for the lights and plug sockets for the garage and ‘office’ (actually a section of the garage he set aside with a stud wall).

For details there are following circuits in use (I went into garage roof to check the cables)
A) Outside Lights, 6Amp MCB, C60HB…….Radial Circuit using 1mm2 T&E cable going to PIR and three outside lights (180W).
B) Office Lights, 6Amp MCB, C60H…….Radial Circuit using 1.5mm2 T&E cable going to 2 Florescent lights (140W).
C) Unused/NC, 20Amp MCB, C60HB…….No circuit, no cables
D) Garage Lights, 10Amp MCB, C60H…….Radial Circuit using 1.5mm2 cable T&E going to 13 Florescent lights (1000W).
E) All the Sockets, 20Amp MCB, C60HB…….Two separate Ring Circuits (one to office one to garage) using 2.5mm2 T&E cable, going to 8 Sockets in Garage and 4 sockets in Office.

I only use small power tools and the lights and not had any issues with the garage, but I wanted to know why I have “C60HB” and “C60H”. So my questions are:
1) I know what a “Type B” MCB is and I presume that this is shown by the “C60HB”, but What Type are the MCBs that say “C60H”?
2) Why are there two types of MCB in use “C60H & “C60HB””?
3) Should I get the MCBs that say “C60H” changed to be type B (C60HB) so they are all the same, or the reverse, or simply ignore as all is working?

Thanks, SFK

 

[Taylortwocities]

Back in the past MCBs were denoted "Type 2", Type 3, etc depending on their characteristics.

A new standard for MCBs came into play on 01/07/1994.
The standard changed from BS3871 to BS EN60898.
Manufacturers were allowed to continue production at the old standard untill 30/06/1999.
For those 5 years, the MCBs could be made to either or both standards.
The trip times of the MCBs are different, and they sometimes overlap.
Type B equates to Type1/2.
Type C equates to Type2/3.
Type D equates to Type 4.


You can see this by reading the MCBs in your photo!

Type 2 is the samish characteristic as B. You will only be able to get B curve MCBs today so HB is what you need.

 

[SFK]

Dear Taylor,
Thank you for that explanation.
Perfect and simple ...... Type 2 sameish as Type B.
Sounds good and makes me happy as gives me confidence that all have about the same response.
The only unanswerable question now is why someone put two Ring Circuits into one MCB when there is a spare/unused MCB.
Thank you again, SFK

 

[Taylortwocities]

The only unanswerable question now is why someone put two Ring Circuits into one MCB when there is a spare/unused MCB.

How do you know they are two ring final circuits?
It may well be one (original) ring circuit that someone has added a couple of radial circuits to.
You would need to carry out continuity tests on the four cables in question to determine what is really going on!

 

[SFK]

Dear TTC,
You are correct regarding "How do you know they are two ring final circuits" and I admit that I am not sure.
But as the wiring is 100% exposed in loft space I can easily follow the cables and see: one ring of 2.5mm2 cable going in and out of distribution board and going to the Sockets in the garage; and a second ring of 2.5mm2 cable going in and out of distribution board and going to the Sockets in the 'office' section of the garage. So I think (in this case) it is a safe assumption for the moment.
As said, no idea why this is the case, I can only guess someone thought it was a good idea in the past (perhaps the now Unused MCB was in use for something else).
SFK

 

[Taylortwocities]

It should be investigated. Here is what can happen:

Single cable (2.5mm²) is added to a ring final circuit as a spur. This is done at the 32 amp MCB. This cable is connected to a double 13A socket as the supply to the garage.
All of this is fine.
Some time later, several more sockets are added to the existing garage socket. This is NOT correct as only one socket can be connected as a spur, unless secondary over-current measures are taken.

 

[SFK]

Dear TTC,
Got it - and yes I would not be happy with that. So I will get the circuit tested as it might be useful to put the 'office' Ring onto the Unused MCB.
However, just to be clear I can see (outside the Distribution Box) that there are two distinct ring circuits going from the Distribution Box to the office and garage. There are no visual breaks in the ring (needs testing of course), there are no radials, there are no spurs, it all seems to be 2.5mm2 cable, and I can follow the exact path of the cable in and out of each of the sockets. So from a visual check each of the two rings circuits goes:
Distribution Box ---- Socket in Garage ---- Socket in Garage ---- Socket in Garage ---- Socket in Garage ---- Distribution Box
and
Distribution Box ---- Socket in office ---- Socket in office ---- Socket in office ---- Socket in office ---- Distribution Box

Of course I have not looked into the Distribution Box so I have not seen if the two ends of each Ring Circuit all go into the MCB (ie there is the possibility that only two of the four Cables go into the MCB resulting in two Radials). Something to be checked I suppose.

SFK

 

[EFLImpudence]

As the MCB is 20A, it does not matter whether the circuit is:

One ring (joined in board), two rings, one ring and two radials or four radials.

All are suitably protected.

 

[SFK]

TTC, Just reading you message again. I think I read it wrong when I responded and sorry about that.

Are you worried that "the supply to the garage is coming my from house" when you say "This cable is connected to a double 13A socket as the supply to the garage"?

To confirm, the supply to the garage is not from the house -the garage has its own direct dedicated supply cable and its own meter. There is no connection to the house whatsoever.

SFK

 

[Taylortwocities]

And my apologies. I hadnt looked at the photo properly. As EFLI says. The socket MCBs are 20A, so everything is properly set up, unless you need to pull more than a total of 20amps on a socket circuit!

 

[SFK]

Dear TTC and EFLI,
With thank to you both for your interest. Thank you for confirming all (probably) okay, I will get it checked out anyway next time.
Regards SFK

 

[kai]

With that loading, you can probably run it from your house, and cancel the dedicated Garage supply, and save one set of standing charges in the process - the charge for a 3 phase supply may be higher than normal single phase feeds.

Is the system earthed? - Notice the lack of earthing cables?

 

[Iggifer]

With that loading, you can probably run it from your house, and cancel the dedicated Garage supply, and save one set of standing charges in the process - the charge for a 3 phase supply may be higher than normal single phase feeds.

Is the system earthed? - Notice the lack of earthing cables?

Possibly TT. Can't quite see the mA of that RCCB but chances are it's 100mA

 

[SFK]

Kai,
With thanks for the suggestion regarding running cable from house. However cheaper not to bother as I am on a cheap standing charge, and unfortunately would be prohibitively expensive and disruptive to run a new cable though house and under patio.
I seem to remember that there is a earth spike (is that right name) in ground on other side of wall with a earth cable leading towards box, but i will add it to list of things to check.
Thx, sfk

 

[Iggifer]

10 points to me!