17th ed question

[1983]

Nuisance tripping from a large transformer installation can be prvented by

A- the use of an rcd
B- the use of a c type mcb
C- the use of a b type mcb
D- the use of a d type mcb

i know the answers is D but can some please point out where in the regs to find the answer

 

[jeremy]

How big is "large". I thought that Ds were for the likes of welding equipment and x ray machines

 

[1983]

2 honest mate i havent got a clue i was revising for my 17th ed exam and got some pass papers which i came across this question i got the answers but doest point out where in the regs the answer is. All i know is Type B - trips between 3 and 5 time full load current
Type C - trips between 5 and 10 times full load current
Type D - trips between 10 and 20 times full load current

 

[Deleted member 26818]

Are you sure the answer is D?
I thought that overload protection could be ommited on transformers.

 

[1983]

im not 100% sure the answewr is d iv just got the questions and answers thats why i wanted 2 check it in the regs just 2b sure im hoping some one on here will be able to help

 

[Guest123]

I thought that overload protection could be ommited on transformers.

On the secondary side, yes, but only for 'safety reasons'

433.3.3 (iii) (green)

Of the 4 options there, I would say D is correct.

 

[telectrix]

i suppose it depends on the current rating of the tranny wrt that of the MCB, either a c type or a d type could be rhe answer.

 

[Deleted member 26818]

The installation, is fed from a transformer, so that would be the secondary side wouldn't it?
If overload protection can be ommitted, fault protection would still be required.
I can't actually think of any Regulation that deals with using type B, C or D MCBs on a transformer.
Could it be that the answer is to not use an MCB at all, and just use an RCD?