understanding tables in OSG and 17th regs book???

[joe1966joe]

hello just taken my Am2 exams last week and past everything apart from the 30 question online exam. I have booked myself in for a resit of the questions for next friday.

questions like...

50mm by 50mm metal trunking fixed horizontally over 20m, how many fixings would it need?

that was one of the questions, i found table 4d in the OSG page 115, but cant get my head around how to read it???

also how do you work out cable factors for use in conduit or trunking???

there were a few more but cant think of them at the min but hopefully they might come back to me by friday or else theres £70 down the toilet again!!

any help would be much appreciated!

 

[xraytek]

50mm by 50mm metal trunking fixed horizontally over 20m, how many fixings would it need?

Table says 0.75m so divide 20m by 0.75m gives you 27 fixings

also how do you work out cable factors for use in conduit or trunking???

Look at the cable factors i.e stranded 6mm thermoplastic= 21.2
Add up the factors for all the cables that will go in the trunking, e.g. if 6 x 6mm pvc cables= 127.2
Choose trunking with a factor greater than or equal to the combined cable factor e.g. cable factor 127.2 permits trunking 50x38 to be used as the trunking factor is higher than 127.2

I think thats right?

 

[joe1966joe]

thanks for that, i might sound stupid here but what does 300 < A < 700 mean? in the table 4d? how does 50mm by 50mm fit into that?

thanks

 

[xraytek]

I means 'A' must be greater than 300 but less than 700.
I dont know why though, where does it say that?

 

[joe1966joe]

it says it in table 4d, where you got the distances from for the fixings. i just get how 50mm by 50mm fits into that??

 

[gutterball]

50x50=2500
that would make the supports 3.0 so 7 supports

 

[JUD]

50x50=2500
that would make the supports 3.0 so 7 supports

It's actually the one above:

1500 < A ≤ 2500 (Greater than 1500 and less than or equal to 2500.)

So the answer is 1.75m (11 supports)

 

[gutterball]

your right it's the one above. shouldn't be looking at regs when I'm half asleep

 

[joe1966joe]

Thanks for that guys, I finally understand it ha! next step fridays resit!

 

[xraytek]

Table says 0.75m so divide 20m by 0.75m gives you 27 fixings

I was close

 

[SirKit Breaker]

If you are having problems using the tables, then you should be asking you tutor to explain them to you clearly until you grasp it.

Cheers...........Howard