single wired armour

[snowplough]

Hi Guys,

Just wondrerd if you could give me any ideas or where to look , trying to answer an old 2391 test question,

Q. What 5 things would you inspect on s.w.a fastened to cable tray,but it asks spec in regards to the cable and not construction of the tray.

Iappreciate your help

Locket

 

[pushrod]

Cables of correct current carrying capacity; security and spacing of fastenings on vertical and horizontal - max distance will be different vertical compared to horizontal. spacing between cable if more than one could interfere with CCC and correct segregation of band 1 and 11 circuits if applicable; Any internal bending radii correct; correct for ambient temps. Any joints and connections mechanically good and accessible for inspection.

Don't be put off by the tray just think for any cables

edit : btw the S in SWA stands for steel

 

[Deleted member 26818]

Don't forget correct making off of the gland, and presence of earth fly lead.

 

[snowplough]

Many Thanks Push rod,

Does segregation of band 1 and 11 only apply to trunking or can it apply to cables on tray as well?

My lecturer once told me at college, no matter what any one says S.W.A stands for Single W.... A not Steel W.... A........

What do you think


Many Thanks

Locket

 

[Deleted member 9648]

So why is aluminium wire armoured termed AWA?

 

[pushrod]

Many Thanks Push rod,

Does segregation of band 1 and 11 only apply to trunking or can it apply to cables on tray as well?

There needs to be a physical partition between them on tray reg 528.1 (iv)
There is also aBS standard about it i think.

My lecturer once told me at college, no matter what any one says S.W.A stands for Single W.... A not Steel W.... A........

What do you think

I'm no expert but Brian Scadden (author of loads of books) is, and he abbreviates steel wired armour to swa so i'll go with him

Many Thanks

Locket

Cheers Locket - just hit the "thanks" button now and again

edit : oops just saw you did - .

 

[Deleted member 26818]

Actually, there doesn't have to be a physical partition.
Segregation can be achieved if the ELV cable insulation is rated at or above the LV rating.

 

[pushrod]

Actually, there doesn't have to be a physical partition.
Segregation can be achieved if the ELV cable insulation is rated at or above the LV rating.

Quite correct. Not experienced in recognising band I circuits being run in band II/low voltage cables mind - would they be immediately noticeable or would you just assume they were band II in the first place - if you know what i mean.

 

[Deleted member 26818]

If there is nothing on the cable stating it's rating, I will assume it's not appropriately rated.
SWA for instance is generally rated to 1000V, and industrial Beldon type (twisted pair, cat 5 etc.), is 300V.
Whereas burgular alarm/phone cable generally has nothing on it.
Obviously when being installed the cable rating should be known, prior to installation and appropriate measures taken.

 

[johnboy6083]

on jobs ive been on,weve hadto run armoured 5 pair and 1 pair, and they still want segregation. Asfar as im concerned, the cable is insulated for highest coltage present, and its protected by SWA, if there ever was a problem.

 

[snowplough]

Hi wire puller ,
you have got a point,

Changing subject,
Can you tell me, when you have a high Zs value and you your measured value is higher after rule of thumb ,

3 ways to get Zs down
Am i right in thinking you can change protective device for one that gives a smaller Zs

Shortening the length of the circuit, making just R1 shorter or R1+R2?

Making the csa bigger, is that the csa of R1 ,or the csa of R1 +R2

Hope you can help, im revising for 2391 on thurs.

Many thanks

Locket

 

[pushrod]

Hi wire puller ,
you have got a point,

Changing subject,
Can you tell me, when you have a high Zs value and you your measured value is higher after rule of thumb ,

3 ways to get Zs down
Am i right in thinking you can change protective device for one that gives a smaller Zs


I think you mean a PD that allows a larger Zs eg changing a c type mcb to a b type
Shortening the length of the circuit, making just R1 shorter or R1+R2?

Making the csa bigger, is that the csa of R1 ,or the csa of R1 +R2

Hope you can help, im revising for 2391 on thurs.

Many thanks

Locket

Often doing the actual calculation instead of using the rule of thumb allows more leeway.

Shortening the circuit length will affect R1+R2. Incidentally upgrading (if needed) the meter tails and the main earth can also lower measured Zs .

Increasing the CSA of either line or cpc, mostly likely both, if you are increasing cable size, will reduce resistance and so reduce Zs.

 

[Deleted member 26818]

Another option is to install supplementary bonding.

 

[snowplough]

Many Thanks Pushrod,

Iincidently when you say decreasing circuit length will effect R1+R2, I take it you meant it will also lower Zs ,

Many Thanks

Locket

 

[snowplough]

Many Thanks Pushrod,

Iincidently when you say decreasing circuit length will effect R1+R2, I take it you meant it will also lower Zs ,

Many Thanks

Locket