Why use SWA to feed DBs?

[s harris]

Hi

Is there any advantage to using SWA cable for a distribution circuit to a DB, instead of eg. using singles in trunking? Let's say the sub board is in the same building as the main board.

It's just whenever I see descriptions of distribution circuits, they seem always to be in SWA (even if not buried underground) and I'm not sure why.

Not a real world problem, I'd like to know for an assignment.

Thanks

 

[James]

singles in trunking are more expensive, also swa has a higher current capacity than singles for the same size cable

 

[Julie.]

In an industrial situation, using steel conduit or trunking is exactly the same as swa, in practical terms though most will carry swa in stock, whilst not the larger cable sizes in singles which are likely to be larger cross section than xlpe swa.

In a residential situation however, in practice the cables would require rcd protection unless run in steel conduit or via swa.

 

[s harris]

That's great, thanks both!

 

[davesparks]

By running a seperate cable you can reduce (or even avoid) the need for grouping factors to be applied to both the distribution circuit and the final circuits.

Distribution circuits can be run in singles, and indeed they sometimes are, especially if it is a shortish distance.

Running large circuits in trunking can also dramatically increase the required size of trunking plus it can be a pig to get the cables round bends!

 

[pc1966]

Unless you have trunking in for other reasons, it is far cheaper/faster/easier to run a length of SWA in.

If you do find yourself running large singles in trunking then using flexible tri-rated will make your pain less, subject to proper use of ferrules and crimp lugs to match!

 

[s harris]

By running a seperate cable you can reduce (or even avoid) the need for grouping factors to be applied to both the distribution circuit and the final circuits.

Distribution circuits can be run in singles, and indeed they sometimes are, especially if it is a shortish distance.

Running large circuits in trunking can also dramatically increase the required size of trunking plus it can be a pig to get the cables round bends!

Thank you Davesparks, I hadn't even thought about grouping. Very useful post, thanks.
[automerge]1595443421[/automerge]

Unless you have trunking in for other reasons, it is far cheaper/faster/easier to run a length of SWA in.

If you do find yourself running large singles in trunking then using flexible tri-rated will make your pain less, subject to proper use of ferrules and crimp lugs to match!

Thank you pc1966 for the info. I'm pretty sure I will go with swa. Am now going to look up flexible tri-rated though. It could be the one I want for some of the other circuits! I wonder if it comes under the classification of 'flexible cable' rather than 'unsheathed' (for those tables)...thanks again, suki

 

[pc1966]

I wonder if it comes under the classification of 'flexible cable' rather than 'unsheathed'

Normally I would consider them as for singles.

Often tri-rated is OK to 105C (UL rating) or 90C (BS 6231 rating) but most accessories are not, so you might be safest to use tables for 70C singles if that is what the end points are safe to.

 

[s harris]

Normally I would consider them as for singles.

Often tri-rated is OK to 105C (UL rating) or 90C (BS 6231 rating) but most accessories are not, so you might be safest to use tables for 70C singles if that is what the end points are safe to.

Thank you for the information pc1966!

 

[Lucien Nunes]

Distribution circuits often travel a significant distance through a building, further than a typical final circuit. Once each circuit leaves the area of the main DB, it is likely to be the only cable following that route. Therefore, a sheathed cable that requires no time-consuming or costly containment to protect it is likely to be the most practical and economic option.

Singles in trunking come into their own when many circuits are to be run along the approximately the same route. The time and cost of erecting the trunking is then justified by avoiding the need to make off each SWA, and of course much neater. Compartment trunking can serve other types of cabling too e.g. data and alarm, further justifying its cost.

 

[s harris]

Distribution circuits often travel a significant distance through a building, further than a typical final circuit. Once each circuit leaves the area of the main DB, it is likely to be the only cable following that route. Therefore, a sheathed cable that requires no time-consuming or costly containment to protect it is likely to be the most practical and economic option.

Singles in trunking come into their own when many circuits are to be run along the approximately the same route. The time and cost of erecting the trunking is then justified by avoiding the need to make off each SWA, and of course much neater. Compartment trunking can serve other types of cabling too e.g. data and alarm, further justifying its cost.

Thank you for this interesting post, Lucien Nunes. The way you've articulated this has improved my grasp of how this works. Thanks!

 

[Dustydazzler]

Swa is a darn site cheaper & quicker to install than building a galv trunking system for a single use...