10mm see protected by 60 switchfuse

[Bellendian]

Hi,

I'd planned to use 10mm see to supply an annex protected by a Wylex 60a switchfuse.

Cable calls suggest that 10mm swa ref method d is good for 60a, even when using the 70deg tables.

Instructions with the Wylex switchfuse state that termination are only good for 16 to 35mm cables though....

Am I missing something here? Should I be using 16mm see for this even though my calls are telling me 10mm is fine?

Cheers

 

[Octopus]

Cable length? load? installation method? earthing type?

Not sure I'd be putting 10mm on a 60A breaker!

 

[Ian1981]

Hi,

I'd planned to use 10mm see to supply an annex protected by a Wylex 60a switchfuse.

Cable calls suggest that 10mm swa ref method d is good for 60a, even when using the 70deg tables.

Instructions with the Wylex switchfuse state that termination are only good for 16 to 35mm cables though....

Am I missing something here? Should I be using 16mm see for this even though my calls are telling me 10mm is fine?

Cheers

Have you applied the 0.9 correction factor using reference method D for underground cables requiring overload protection?
See section 433 in bs 7671 regarding overload protection.

 

[Deleted member 9648]

What about volt drop?

 

[Bellendian]

Hi, volt drop is ok, not a long run and within 5% for distribution cct, I think Ian may have it though, since the 70deg tables list ccc using ref method d as 60a dead, so no room for manoeuvre with the 0.9 factor.
Having said that the cable would be xlpe so actually capable of more...only issue being the 90deg at terminations, but cable clipped direct leading into terminations so in theory ok there as well! Gut instinct saying use 16mm and not worry...but part of me thinking why if 10 will do the job...

 

[Ian1981]

Hi, volt drop is ok, not a long run and within 5% for distribution cct, I think Ian may have it though, since the 70deg tables list ccc using ref method d as 60a dead, so no room for manoeuvre with the 0.9 factor.
Having said that the cable would be xlpe so actually capable of more...only issue being the 90deg at terminations, but cable clipped direct leading into terminations so in theory ok there as well! Gut instinct saying use 16mm and not worry...but part of me thinking why if 10 will do the job...

If you plan to have lights then your still restricted to 3% VD as it’s from the origin of the installation to the current using equipment Or lights in this case.
You could plan for 2% VD on your distribution circuit leaving 1% for lights or vice verse.
Unless you’ve got dead on 230 volts at your origin then it’s probably not an issue unless your run is rather large

 

[Toneyz]

What would be the design load?

 

[Bellendian]

Hi, design load 55a after diversity. I've gone for 16mm....not worth the risk for the small cost difference between 10 and 16mm cable!
I am trying to understand the reasoning behind the 0.9 correction factor for buried cables though....
The ccc tables are done using an ambient of 20 degc when buried, but the implication of having to factor that down is that the cables are actually expected to be in a warmer ambient than that? That surprises me to be honest, so if anyone could shed some light on this it would be appreciated!

 

[Andy78]

Hi, design load 55a after diversity. I've gone for 16mm....not worth the risk for the small cost difference between 10 and 16mm cable!
I am trying to understand the reasoning behind the 0.9 correction factor for buried cables though....
The ccc tables are done using an ambient of 20 degc when buried, but the implication of having to factor that down is that the cables are actually expected to be in a warmer ambient than that? That surprises me to be honest, so if anyone could shed some light on this it would be appreciated!

There is no heat dissipation possible when the cable is directly buried, and the surface layers of ground will always be warmer than ambient air temps.

 

[Spud28]

I had a similar scenario, opted for the 10mm xple though, cable calcs worked out ok and CCC worked out at over 63A

 

[Spoon]

I had a similar scenario, opted for the 10mm xple though

I know you probably already know this, so it's just a reminder:
When using 90 deg cable just make sure all the devices connected to the cable are also suitably rated for 90 deg. See 512.1.5 (page 117 BYB)