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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 8th Feb 2015, 10:43 am   #1
mark_in_manc
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Default Crabtree C50 MCBs

Hi folks

I've just come by a rank of 6 of these mounted in a steel box with a master on/off, looking like they might have once formed part of a domestic installation - and rather well-made it all seems. From a bit of a Google, I glean that the trip times may or may not meet current standards - but presumably the protection offered is considerably superior to a piece of fuse wire. Any thoughts?

Obviously no-one would want to advise anyone to actually install anything which didn't meet current () requirements ...

cheers
Mark
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Old 8th Feb 2015, 12:30 pm   #2
ukcol
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Default Re: Crabtree C50 MCBs

Here are the B,C and D curves for circuit breakers taken from the 17th Edition.
It includes the curve for your 50 Amp type C breakers.

I'm sorry that the quality of the scan is not that good.
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File Type: pdf B,C & D curves from 17th Edition..pdf (301.9 KB, 226 views)
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Old 8th Feb 2015, 1:28 pm   #3
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Default Re: Crabtree C50 MCBs

MCB's are only resettable fuses - the protection they offer isn't that much greater than an ordinary wire fuse (both of which protect the cable, not the equipment).

If safety is of paramount importance (and it should be) then RCD's are the basic minimum requirement for 'proper' safety.
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Old 8th Feb 2015, 2:28 pm   #4
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Default Re: Crabtree C50 MCBs

The curves shown above are for BS60898 the C50s will be BS3871.

BS3871 isn't used now but is perfectly fine as long as your circuits meet the required disconnection times. For almost all household circuits that will be 0.4 seconds. As mentioned above a 30mA RCD will be required for most, if not all circuits in a domestic property. RCD main switches were made for the C50 range as were RCBOs, both are now quite rare.

These boards are reliable and well made, but from a professional point of view should be replaced with a more modern one, containing at least 2 RCDs to split the circuits, or better still RCBOs. The type of earthing used will also affect the types of components used. The 17th edition third money making scam, sorry, amendment, of the regulations will soon change the types of consumer units allowed in domestic properties:

EDIT:
To clarify C50 is the range number not Type C 50 Amp! These will be Type 2,3 or 4.

Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439 3 and shall:
I. Have their enclosures manufactured from non-combustible material, or
II. Be enclosed in a cabinet or enclosure constructed of non-combustible material and complying with Regulation 132.12.
Note 1: Ferrous metal e.g. steel is deemed to be an example of a non-combustible material.
Note 2:* the implementation date for this regulation is the 1st January 2016. This does not preclude compliance with this regulation prior to this date.

Last edited by matthewhouse; 8th Feb 2015 at 2:38 pm.
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Old 8th Feb 2015, 3:24 pm   #5
ukcol
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Default Re: Crabtree C50 MCBs

Quote:
Originally Posted by matthewhouse View Post
To clarify C50 is the range number not Type C 50 Amp! These will be Type 2,3 or 4.
Opps
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Old 8th Feb 2015, 7:41 pm   #6
Aaamusements
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Default Re: Crabtree C50 MCBs

Thousands of these are still installed in various locations, including but not limited to pretty much every military establishment the length of the country!

The last time I had some spares they were quickly snapped up by a buyer.
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Old 27th Feb 2015, 6:03 pm   #7
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Default Re: Crabtree C50 MCBs

Any photos please?
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Old 29th Mar 2015, 12:29 am   #8
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Default Re: Crabtree C50 MCBs

These mcbs were very popular from the late 1960s right through to the early/mid 1980s.

The were made to the 1965 bs3871 standard, and were
often used in commercial applications, in either single or three phase metal distribution boards, in a dark green colour up to 1981 and thence birch grey up to the end of the range in the mid 1980s, when the newer Crabtee Starbreaker and polestar range switchgear replaced them.

There was a domestic range of boards made by Crabtree that used them, with a hardwood back frame, and hard Bakelite cover, in the early 1970s.

The majority of schools, offices and commercial buildings built in the 1970s used them.

Another brand, popular at the time was Dorman Smith.
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Old 4th Apr 2015, 12:34 pm   #9
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Default Re: Crabtree C50 MCBs

Quote:
MCB's are only resettable fuses - the protection they offer isn't that much greater than an ordinary wire fuse
I beg to differ. MCBs and HRC cartridge fuses are known as 'close protection' devices that offer enhanced protection over replaceable fuse wire. The IEE (IET) regulations make allowances in reference tables for the choice of cables and circuit loading you can make depending on the type of protective device and earthing arrangements.
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