Hi,
Quike question relating to details listed on M.C.B's (probably really obviouse)
I am undertaking periodic test/inspection and have come across an old Square d Type QO-X MCB.
It is listed as a BS3871 Part 1 with an instantaneous trip type 4,
catagory of duty M3.
The questions I have are these:
Does the part 1 info mean type 1? or is it a Type 4 as mentioned further down the list? Type 4's do not appear in the onsite guide however! I know BS 3871 are no longer relevant but Type 4's dont appear in the 16th edition onsite guide either!
Secand question:
I thought the duty catagory M3 ment a short circuit capacity rating of 3 kA? Does it not?
But under neath the printed label is stamped 10000 A, is this a s.c.c of 10 kA?
Any advice would be appreciated.

Ok, to answer your question I will give you some information that you can use now and keep for future reference:

BS 3871: Part 1 Circuit Breakers:

Type ::: Instantaneous Trip Current

1 ::: > 2.7 In <= 4.0 In
2 ::: > 4.0 In <= 7.0 In
3 ::: > 7.0 In <= 10.0 In
4 ::: > 10.0 In <= 50.0 In
B ::: > 3 In <= 5 In
C ::: > 5 In <= 10 In
D ::: > 10 In <= 20 In

Category of Duty ::: Prospect Current ::: Power Factor

M1 ::: 1000 A ::: 0.85 to 0.9
M1.5 ::: 1500 A ::: 0.85 to 0.85
M2 ::: 2000 A ::: 0.75 to 0.8

M3 ::: 3000 A ::: 0.75 to 0.8
M4 ::: 4000 A ::: 0.75 to 0.8
M6 ::: 6000 A ::: 0.75 to 0.8

M9 ::: 9000 A ::: 0.55 to 0.6

Markings which should be present are:

a. B.S. 3871.
b. Rated voltage and the associated number of phases.
c. Rated current.
d. Reference calibration temperature.
e. Type, according to instantaneous tripping current.
f. Manufacturer's name or distinguishing mark.
g. Frequency, if other than 50 Hz.
h. Manufacturer's type reference, where more than one type is manufactured.
j. Category of duty.
k. Country of manufacture.

Regards

-------------------------
E & OE

Edited: 26 November 2009 at 01:37 PM by micjamesq