General characteristics

[rich3009]

When doing mock exams 17th edition the questions that always have me stumped are about general characteristics, I had a question with maximum demand and max current in choices, both seemed feasible answers

 

[dmxtothemax]

you need to read the question carefully !
What exactly are they asking
not your interpretation
what are "they" asking - "exactly"
makes all the difference !

 

[westward10]

Maximum demand is generally the figure you obtain after diversity is applied to the maximum current. For example if you have three 32A ring final circuits their maximum current demand could theoretically be 96A but in reality this is not likely to happen so you apply diversity to come up with a maximum demand figure.

 

[rich3009]

Right so what they are looking for is a design figure not an absolute, but in characteristic of design max current would be a consideration to arrive at max demand

 

[rich3009]

Heres another strange one
7 o/c 4 - Which of the following items does not offer ‘basic’ protection:
a a circuit protective conductor.
b a socket outlet.
c a lampholder.
d equipotential bonding conductors

 

[westward10]

Have you looked up the meaning of basic protection.

 

[rich3009]

Yes a few of those are nothing to do with basic protection, the lampholder is the obvious one, but other answers would be correct a. And d . are for automatic

 

[westward10]

Have a look through Reg 416 of BS7671.

 

[rich3009]

What does bonding and cpc have to do with fault free conditions

 

[rich3009]

Three of those answers do not offer basic protection

 

[Andy78]

Three of those answers do not offer basic protection

Basic protection is protection against contact with live parts. Of those answers how many are concerned with live parts ? And of those, which offer basic protection and which don't ?

 

[rich3009]

It's a fair point unless you interpret the question as checking your knowledge of the difference between fault and basic protection

 

[westward10]

It is posing the question to see if you understand the meaning. Reg 416 will help you.

 

[rich3009]

If a fault occurs in the HV system and a magnitude of fault voltage of 430v occurs between exposed conductive parts and earth on the LV installation, what is the maximum tolerable duration of the fault

 

[rich3009]

What part of the regs is this

 

[Spoon]

If a fault occurs in the HV system and a magnitude of fault voltage of 430v occurs between exposed conductive parts and earth on the LV installation, what is the maximum tolerable duration of the fault

Have a look at Reg 442.2.2 mate

 

[rich3009]

25) If a fault occurs in the HV system and a magnitude of fault voltage of 430v occurs between exposed conductive parts and earth on the LV installation, what is the maximum tolerable duration of the fault
a) 10ms
b) 100ms
c) 200ms
d) 300ms

I don't know how to answer this one

 

[westward10]

What needs to happen generally under fault conditions, disconnection (ADS). You are looking for disconnection times.

 

[rich3009]

Do you know the answer and how it's derived

 

[westward10]

Have you not tried looking up disconnection times.

 

[rich3009]

Doesn't help

 

[westward10]

411.3.2

 

[rich3009]

Is it 10ms based on greater than 400v on a TN system and tolerated as in human heart, I thought it was cable fire. duh

 

[rich3009]

Or is 0.1s 100ms in real money crap at decimal conversion