Swa current carrying capacity

[fattony]

hi

I've been asked to pick up a job where the previous builder went into liquidation and the property management company is asking me to complete the electrical works, relocate a fuseboard.

Everything the previous company has done is exceptionally neat but I'm concerned on the design front with the SWA, the supply from the mccb panel is 100A and the new swa they have pulled in is 16mm 4c (TPN) looking at the guides on the web current carrying capacity for this clipped direct is 94A, struggling to remember the exact formula would have to go through the books but is the 94A a guide and you can calculate it exactly?

Would rather not derate the mccb, and it's virtually impossible to rewire without taking ceilings down

Thanks

 

[Wilko]

Hi - worst case is 3phase 70C rated then 16mm clipped direct is 77A, but if you are only using single phase of the cable it's 89A. If the cable is 90C rated then its 94A and 110A respectively. Hope that helps

 

[Midwest]

Don't the 90' thermosetting cables have to be used with similar accessories/equipment to have the higher ccc?

 

[Wilko]

Yep, that's the next hurdle ... sorry to say, but for a 100A supply I'd start with 25mm as min.

 

[Midwest]

Life's never easy now, is it

 

[westward10]

Does it need 100A, I suspect you could derate the mccb.

 

[telectrix]

Does it need 100A, I suspect you could derate the mccb.

that would be my prefernce.

 

[Andy78]

If it's a MCCB the chances are the 100A (max) device may wind down to 80A ?

 

[bigspark17]

What your mac demand looking like taking diversity into account.? Id go with others and say derrating the mccb may be the way forward if the install could work off lower rated mccb

 

[fattony]

Thanks, I'm going to propose we change the mccb to a 63A, it's the easiest way

 

[davesparks]

Thanks, I'm going to propose we change the mccb to a 63A, it's the easiest way

Why not just wind it down a bit? That may be what the original design specified in order to keep some characteristic of the 100A device which the 63A can't provide?

 

[fattony]

To be honest I wasn't aware you could just wind it down, having researched them a little I understand there is a pot on them which allows you to adjust the current setting

Thanks

 

[westward10]

Some you can but not all.

 

[davesparks]

To be honest I wasn't aware you could just wind it down, having researched them a little I understand there is a pot on them which allows you to adjust the current setting

Thanks

Then I'd suggest getting the advice of someone who knows what they are doing, there's usually adjustments on both magnetic and thermal tripping characteristics. You're outside the territory of plug and play fixed protection now.

 

[Spoon]

Then I'd suggest getting the advice of someone who knows what they are doing, there's usually adjustments on both magnetic and thermal tripping characteristics. You're outside the territory of plug and play fixed protection now.

I see by your wonderful post that teaching people new things just isn't your style...

 

[davesparks]

I see by your wonderful post that teaching people new things just isn't your style...

I am more than happy to teach new things, but I don't think I can put enough information in to a post on here to explain this properly.

 

[fattony]

It's a strange setup this, I'm doing the work on behalf in the managing agent so only looking at landlords side, there is another sparks working for the fit out company and for some strange reason they didn't want him to take on all the works.

I wanted to pull the cables back through the galvtrunking on the 2nd floor and get a hole through the floor (builders works) dropping into the board in copex, told no holes through the floor.

So we ran 24 circuits through the first floor, up the riser to the existing db location for a junction box, din rail connectors

Literally about to start stripping out the db ready for the junction box to be told that there is no room for a junction box in the riser and I should have pulled the cables back through the 2nd floor, ffs!

Fortunately client is on my side this route was discussed and agreed but I've got to pull it all out and start again.

In the new db the other sparks was intending on fitting a meter, I have now found out the 16mm swa is a sub main off another board hence the meter, the meter looks like it needs a connection for power but I'm not sure where to connect it, are they fuses on the bottom right and I need to come off the main switch?

View attachment 35397

 

[Leesparkykent]

It's a strange setup this, I'm doing the work on behalf in the managing agent so only looking at landlords side, there is another sparks working for the fit out company and for some strange reason they didn't want him to take on all the works.

I wanted to pull the cables back through the galvtrunking on the 2nd floor and get a hole through the floor (builders works) dropping into the board in copex, told no holes through the floor.

So we ran 24 circuits through the first floor, up the riser to the existing db location for a junction box, din rail connectors

Literally about to start stripping out the db ready for the junction box to be told that there is no room for a junction box in the riser and I should have pulled the cables back through the 2nd floor, ffs!

Fortunately client is on my side this route was discussed and agreed but I've got to pull it all out and start again.

In the new db the other sparks was intending on fitting a meter, I have now found out the 16mm swa is a sub main off another board hence the meter, the meter looks like it needs a connection for power but I'm not sure where to connect it, are they fuses on the bottom right and I need to come off the main switch?

View attachment 35397

Sounds like a right pain in the backside job mate.

 

[fattony]

Sounds like a right pain in the backside job mate.

It is, wish I never got involved, I've had to connect the swa to a temp board for now, when they fit the new board they will re terminate my swa, I could pull 3 circuits back through the first floor but I'm not touching the 2nd floor without another order, will test what I've done and close the job as far as I'm concerned, once they've argued it I'll go back and change it, means this will get stripped out though

View attachment 35398

 

[Chr!s]

hi

I've been asked to pick up a job where the previous builder went into liquidation and the property management company is asking me to complete the electrical works, relocate a fuseboard.

Everything the previous company has done is exceptionally neat but I'm concerned on the design front with the SWA, the supply from the mccb panel is 100A and the new swa they have pulled in is 16mm 4c (TPN) looking at the guides on the web current carrying capacity for this clipped direct is 94A, struggling to remember the exact formula would have to go through the books but is the 94A a guide and you can calculate it exactly?

Would rather not derate the mccb, and it's virtually impossible to rewire without taking ceilings down

Thanks

Hi, id suggest probably okay, the designer may have tweaked the factors applied to the cable ccc, if so you can get it above the 100 amp.