1970s fuseboard advice

[Barnet Al]

Went on a griefy job today, simple oven swap but couldn't isolate circuit as no labels, or supply because owner was on a video call. Also no local isolator for the oven. Anyway, would appreciate some advice on this relic. Are they plug in BS 3036 replacements? Can I just pull them out? What era are they?

 

[Fleeting]

Crabtree C50. They are circuit breakers screwed to a busbar. 1970s onwards.

 

[Andy™]

there 3871 MCB, not 3036 fuses...

 

[Barnet Al]

That's great thanks! At 50 years old I would be thinking to advise that while I can fit the oven (with a local isolator) they should be replaced as their correct operation cannot be guaranteed? Fuse wire is fuse wire, it will always work, but could you have any confidence in these? Or install an RCBO downstream or better still, walk away?

 

[OnOff]

It looks like this inside. They might be Type 1 & 2 as opposed to Type B & C which had slightly different current curve characteristics. Think it depends on whether white or yellow writing on them.

They are circuit breakers not fuse wire.

 

[Phoenix]

Think the boards were still going in as late as about '89 so could be anywhere 70s - 80s. The writing on the breakers is a little clue to the age, originally white, later ones were yellow, with the white being M3 breaking capacity and the yellow M4.5. All breakers were to BS3871 type 2, however you could still buy the breakers from manufacturer until quite recently (perhaps you still can???) and they were reclassified as 60898 type C for the new ones once 3871 was no longer current, but I don't think they actually changed, just got recertified. Type 2 is instant operation at between 4 and 7x, type C is between 5x and 10x so I presume they would go out somewhere between 5x and 7x.

There were actually RCBOs for them, but they were quite rare, I can count on one hand how many I have come across! (15th edition regs didn't really have many requirements for them!)

They are actually hydralic in operation, they have a little dashpot type thing inside, theres a youtube tear down video by john ward.

Worth recommending a board upgrade as there is no additional RCD protection, but I get the feeling a lot of the C50s will still be working fine when a lot of later stuff has long since failed!

 

[OnOff]

 

[OnOff]

All breakers were to BS3871 type 2

I'm sure I have some here that aren't Type 2.

 

[OnOff]

Some info here on the types:

https://www.tlc-direct.co.uk/Book/3.6.4.htm

 

[OnOff]

More reading with a link to the aforementioned video:

https://flameport.com/electric_museum/old_equipment/crabtree_c50_circuit_breaker.cs4

 

[Murdoch]

If in doubt turn off main switch in CU

When you say owner was on video call, is this a rental property?

 

[binky]

If you are just replacing a cooker, then no need to replace the board. However, if I was you I would strongly recommend a full inspection and board change, plus install an isolator somewhere. If this is a rental, then that is a 'must' to be legally compliant.

As for isolating the cooker, turn the whole board off if you have to

 

[Fleeting]

It looks like this inside. They might be Type 1 & 2 as opposed to Type B & C which had slightly different current curve characteristics. Think it depends on whether white or yellow writing on them.

They are circuit breakers not fuse wire.

View attachment 16950

None of them were type 1. Early devices were 3871 type C, generally not identified as type C. Later devices became 3871 type 2 and always identified, if devices are not identified assume 3871 type C as advised by Crabtree. Production of the distribution boards stopped but Crabtree continued to produce devices badged as 60898 type C as @Phoenix said at least into the 90s and I have only ever seen one.

 

[Murdoch]

It’s always a shame when the OP reviews the threads and doesn’t add or update info

 

[UNG]

Certainly a blast from the past fitted loads of these C50 boards back in the late 70's / early 80's then moved on to installing Merlin Gerin and Hager

 

[OnOff]

I've a fully populated 9 way C50 board here just removed. Plus a few loose ones.

Guaranteed never tripped!

 

[SPECIAL LOCATION]

Went on a griefy job today, simple oven swap but couldn't isolate circuit as no labels, or supply because owner was on a video call. Also no local isolator for the oven. Anyway, would appreciate some advice on this relic. Are they plug in BS 3036 replacements? Can I just pull them out? What era are they?View attachment 16948

I cannot believe that any competent person cannot identify what circuit is supplying a load even if there are no labels are written on the CU..?!

Video calls and/or local isolators are just a red-herring, piss-in-the-wind factor / distraction IMHO...

In this instance, one option is to turn each MCB off until you find the one supplying your load.
Or open up the cover looking for a Larger 6.0mm entering the CU.

(P.S. the Cooker is probably a dedicated circuit)

 

[Barnet Al]

I am really grateful to everyone on the Forum for their advice. I watched John Ward's video and he concluded that they are no better or worse than anything else out there.
I did take the cover off and search for a 6mm radial on one of the 30 amp circuits, but couldn't identify it.
Went back on Friday and was able to speak to the owner this time, turns there are 3 DBs under the stairs, two buried by the owners stuff. DB2 with 2 plug in MCBs and DB3 with 2 RCD protected circuits. The oven was running off DB2. The hob was running off DB3 in 6mm clipped direct with a B40 OCPD. I isolated the cable from DB2 and ran a spur off the isolator for the hob to supply the 15 amp oven. A bit time consuming, battling with cable between 2 voids but the owner was happy with it being on the new DB3 (metal consumer unit) and having one isolator for both (her choice... hope that doesn't start another discussion ....
I didn't want to worry her too much but stressed that she should use a plug in RCD adapter for outdoor electrics, as she plugs her Lawnmower into an outdoor socket with no RCD protection! I didn't notice the halogen spotlights in the kitchen .......... But I suggested a consumer unit upgrade to put everything on 1 board.

 

[kerching]

DB2 and ran a spur off the isolator for the hob to supply the 15 amp oven.

How did you 'fuse down' the 15A spur from the 40A mcb on DB3

 

[SPECIAL LOCATION]

turns there are 3 DBs under the stairs, two buried by the owners stuff.

Hidden, extra small DB's (CU's), in obscure locations, are a common occurrence that you should always keep in mind when undertaking any work on an installation you have no prior knowledge of...

Plus maybe some useful future tips & guidance...

While you are checking on earthing & bonding prior to any alterations/additions as per Reg: 132.16, It is always good to

1/ Locate the suppliers cut-out.
2/ Suss out the earthing arrangements.
3/ Identify if there are any splits/branches in the supply tails and/or sub-mains from the cut-out and/or switch-fuses, to multiple CU's.
4/ Keep your 'common sense head on' knowing what type of circuit arrangement, cable size, protective device you are looking for.
5/ Never trust any CU labels to be correct unless you have identified and proved them to be correct yourself!