BS 88 fuse in a 20A radial socket outlet circuit.

[Jordanh1992]

A BS 88 fuse protects a 20A radial socket outlet circuit. The circuit is wired using 2.5mm2 single core cable installed in a 16m length of PVC conduit. A separate protective device conductor consisting of a 1.0mm2 PVC cable is used. Assuming that no correction factors are applicable and that the value of Ze is given as 0.5 ohms, determine whether the circuit complies with IET wiring regulations for shock protection? The nominal voltage (Uo) may be taken as 230 volts.

How do I figure out if the maximum disconnection time is 0.4 or 5 seconds, so then I can work out what the maximum Zs allowed for a 20a BS 88 fuse is...

Ze = 0.5 ohms
R1 + R2 = 25.51 (table 11 OSG)
Mf = ???
L = 16mm2

Any little tips you guys could give me, I'm new to all this so go easy!
Thanks

 

[KAS1]

Check BGB for disconnection times

 

[telectrix]

hint: the size of cable will tell you the approx. current demand is <32A.

 

[Jordanh1992]

Thanks I'll check now and get back to you

 

[Jordanh1992]

So for a 20a BS 88 fuse with a disconnection time of 0.4 seconds

Uo/Zs - 230/130 = 1.77 ohms?

 

[Outspoken]

A BS 88 fuse protects a 20A radial socket outlet circuit. The circuit is wired using 2.5mm2 single core cable installed in a 16m length of PVC conduit. A separate protective device conductor consisting of a 1.0mm2 PVC cable is used. Assuming that no correction factors are applicable and that the value of Ze is given as 0.5 ohms, determine whether the circuit complies with IET wiring regulations for shock protection? The nominal voltage (Uo) may be taken as 230 volts.

How do I figure out if the maximum disconnection time is 0.4 or 5 seconds, so then I can work out what the maximum Zs allowed for a 20a BS 88 fuse is...

Ze = 0.5 ohms
R1 + R2 = 25.51 (table 11 OSG)
Mf = ???
L = 16mm2

Any little tips you guys could give me, I'm new to all this so go easy!
Thanks

PVC cable...thats not very good as a circuit protective conductor, are you sure it's not PVC insulated copper??

Oh, by the way, if you want to type 1.0mm², to get the 2=² you need to hold the Left Alt key and then type 0178

 

[Jordanh1992]

No the question says its protected by 1.0mm2 PVC cable :/

Im using an iPad so I'm not sure if you can do that.. Thanks anyway

 

[Outspoken]

No the question says its protected by 1.0mm2 PVC cable :/

Im using an iPad so I'm not sure if you can do that.. Thanks anyway

Aha, you could be right about that because I have trouble doing that on my Android tabs!!

 

[telectrix]

and on a laptop without the separate numerical keypad.;lkomujlp;'[98k,.'#';/]]]];;L;[''/'.[OPPP,;./[];-=OLMPL';/'#

 

[Deleted member 72666]

and on a laptop without the separate numerical keypad.;lkomujlp;'[98k,.'#';/]]]];;L;[''/'.[OPPP,;./[];-=OLMPL';/'#

Are you sure tel? Because every time I try that I get this ;lkomujlp;'[98k,.'#';/]]]];;L;[''/'.[OPPP,;./[];-=OLMPL';/'# ! Must be my laptop me thinks!..... I know, I'll bin it and get myself another!

 

[Geordie Spark]

Are you sure tel? Because every time I try that I get this ;lkomujlp;'[98k,.'#';/]]]];;L;[''/'.[OPPP,;./[];-=OLMPL';/'# ! Must be my laptop me thinks!..... I know, I'll bin it and get myself another!

You'll find it only works on a Scouse keyboard.

 

[Adam W]

How come you're using a BS88 if you're worried about disconnection times? I'd use a BSEN60898.

 

[Stroppy]

Coz that's not what the homework question asks!

 

[Jordanh1992]

What's the easiest way of finding out the Mf? Table 12 OSG?

 

[Ducksy]

(Comic guy voice) worst title ever!

 

[Jordanh1992]

Anyone gonna help haha

 

[Jordanh1992]

Am I correct in saying the Mf is 1.02 (table 12 OSG)?

Therefore...
Ze=0.5
R1 + R2= 25.51 table 11 OSG
Mf= 1.02 table 12 OSG
L= 16

0.5 + 25.51 x 1.02 x 16 = 416.82/1000= 0.42

0.5 + o.42 = 0.92

Zs = 0.92 ohms, this is not above the maximum permitted value and therefore is acceptable?

Could anyone check over my answer and see if I'm on the right lines! Thanks

 

[telectrix]

on the 9 and the 0m of your keyboard, by using the shift key, you can get ( and ). then it might look as if it may be correct.

 

[Adam W]

Do your own homework haha