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Could someone help with the age of this DB?

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TheCodboy

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Hi all, my friend has just moved into a property and I've had a quick look at his DB and was greeted with a very old Crabtree board. Could someone give a rough estimate on how old it is? I think it could be one of the oldest ones I've seen. Thanks in advance!!
[ElectriciansForums.net] Could someone help with the age of this DB?
 

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Late 60s-70s. Crabtree C50 series, magnetic-hydraulic MCBs. Still in use in certain places e.g. London Underground. There are older designs of MCBs than those.
 
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Indeed. They have a little sealed hydraulic capsule inside the coil. When overcurrent is present, magnetic flux from the coil creates enough force on the ferrous piston inside to overcome a spring, causing it to move slowly against fluid resistance towards one end of the cylinder. As it moves, it changes which part of the core it magnetically shunts, and in its final position it increases the flux acting on the tripping armature enabling the amount of flux already present to trip the breaker. This creates the timed response normally associated with the thermal element of an MCB. If a fault occurs, there is enough flux to cause the armature to trip the mechanism instantly, without having to wait for the hydraulic unit to respond.
 
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Lucien Nunes said:
Indeed. They have a little sealed hydraulic capsule in the magnetic circuit. When overcurrent is present, magnetic flux from the coil creates enough force on the ferrous piston inside to overcome a spring, causing it to move slowly against fluid resistance towards one end of the cylinder. When it gets there, its position decreases the magnetic reluctance of the circuit enabling the amount of flux already present to operate the tripping armature. This creates the timed response normally associated with the thermal element of an MCB. If a fault occurs, there is enough flux to cause the armature to trip the mechanism instantly, without having to wait for the hydraulic unit to respond.
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They must have been relatively expensive at the time ?
 
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I have some prices somewhere but yes. Hence most of these being found in commercial and industrial boards, with much less uptake into domestic where the additional cost over fuses wasn't thought justfied. These plastic-fronted domestic boards are relatively rare. Someone (Tel? Gerry?) on the forum kindly sent me one for the museum a few years ago.
 
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The protective devices you have are probably BS3871 type C but in some circumstances the white written ones are type 2. You would need to remove each one, type 2 are always printed as such. Some state type C (3871) but if if is not printed assume type C. Crabtree were still producing these up until a few years ago in the guise of 60898 type C they are actually quite rare I've only ever seen one.
 
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nicebutdim said:
Wouldn't you know it. John also posted a video of a C.50 board, albeit a (later?) steel enclosure.
Click to expand...
Saw one last week, as above there are quite a lot of them out there.
What was a first for me was finding a 7.5 amp circuit breaker.

[ElectriciansForums.net] Could someone help with the age of this DB?
 
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7.5A is very common for commercial distribution boards. Not quite sure where the rating is derived from I've considered it the BS3036 equivalent of the 5A fuse (apply the 0.725 correction factor gives you about 7A).
 
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