Advice On A Install

[BangTidy]

Hi, just looking to bounce a few ideas together off people about an install im specing up please?

Install is a 3 phase supply for a cleaning company with industrial machines.
1 x 3PH washer 12kw 32A per phase.
1 x 3PH washer 18kw 45A per phase.
2 x dryers 40A per phase.
2 x 2 gang sockets in washer area.

Equipment is going is going to be located around 30 meters from distribution point. So was looking at installing a sub main nearer the equipment, so from the main DB in 10mm swa 4 core and then from the sub-main in 4mm swa 4 core to associated isolators.

Was wondering for the 10mm if the armour alone is enough for CPC or would need to carry a ajourning CPC? and the correct cable selection being used for the current capacity?

Any feedback appreciated, cheers.

 

[stef]

Usually, the steel armour is sufficient. However, a good practice os run a separate cpc of 6mm with it because steel has diferent properties than copper, glands can become loose, steel can corrode and in the end it doesnz't take much to run a separate earth. At least younhave a cpc with a known cross section. However, with 10 mm you are pushing it a bit, is only 62 A with method E. Don't know how much diversity you could apply.

 

[johnboy6083]

Usually, the steel armour is sufficient. However, a good practice os run a separate cpc of 6mm with it because steel has diferent properties than copper, glands can become loose, steel can corrode and in the end it doesnz't take much to run a separate earth. At least younhave a cpc with a known cross section. However, with 10 mm you are pushing it a bit, is only 62 A with method E. Don't know how much diversity you could apply.

i agree that sometimes running a seperate CPC has its advantatges, especially with buried cables, and cables subject to damage.
Ther way you find out if your SWA is suitable as CPC, is to apply the adiabatic equation.

So lets say you are feeding yopur sub-board with a 50A fuse to BS88(to provide discrimination).

the current required to trip that fuse in 5 secs (its a distribution circuit) will be 220A (fig 3A3, BS7671:2011)

s= (sq rt (i2t))/k

i2= 220x220= 48400
t= 5 seconds
k=51 for swa at 70 degrees (id design to 70 unless you know that the equipment will take a higher temeperature)

the resulting size is 9.64mm2 (steel armour size, not copper)

so a 10mm2 4c will easily comply with a SWA csa of 46mm2.

 

[BangTidy]

Cheers for the replys, the sub main is only really being designed for the equipment that is be installed. Any future additions will be from the main DB, thus all the expected load on that 10mm supply.

 

[telectrix]

i'd run in a 16mm anyway. that will give you the facility for extra load in the future if needed. and agree with previous posts that the armour will be OK as cpc, but a separate earth conductor, belt and braces, is a good idea.

 

[Brightspark2]

Any future additions will be from the main DB, thus all the expected load on that 10mm supply.

The amount of times you hear that and then 3 weeks later you get a call to install more as they realize they want more equipment...

Im jumping on the 16mm bandwagon, armour is fine to use as cpc...

Check your calcs because 4mm doesnt seem adequate for 40-45A either...thats with XLPE too which I'm guessing it is...

Sent from my Xperia S using next doors WIFI.

 

[Chr!s]

i agree that sometimes running a seperate CPC has its advantatges, especially with buried cables, and cables subject to damage.
Ther way you find out if your SWA is suitable as CPC, is to apply the adiabatic equation.

So lets say you are feeding yopur sub-board with a 50A fuse to BS88(to provide discrimination).

the current required to trip that fuse in 5 secs (its a distribution circuit) will be 220A (fig 3A3, BS7671:2011)

s= (sq rt (i2t))/k

i2= 220x220= 48400
t= 5 seconds
k=51 for swa at 70 degrees (id design to 70 unless you know that the equipment will take a higher temeperature)

the resulting size is 9.64mm2 (steel armour size, not copper)

so a 10mm2 4c will easily comply with a SWA csa of 46mm2.

What's strong with the tables? And why are you using 5 sec, you don't know your I2 until you know your Zs.

 

[big show]

I too would go with a 16mm so you have some head room too expand later also maybe weigh up the price of a 5 core if you want it to look prettier so no separate CPc but normally more expensive

 

[johnboy6083]

What's strong with the tables? And why are you using 5 sec, you don't know your I2 until you know your Zs.

i used the 5 secs max disconnection time, and the 'i' figure was the min current required to fuse a 50A bs88 in 5 secs. Obviously this is worst case scenario with Zs on the limit, and fault current at the minimum.
As you know, a decrease in impedance causes a rise in fault current, which in turn reduces the time it takes for the protective device to operate.

 

[Chr!s]

i used the 5 secs max disconnection time, and the 'i' figure was the min current required to fuse a 50A bs88 in 5 secs. Obviously this is worst case scenario with Zs on the limit, and fault current at the minimum.
As you know, a decrease in impedance causes a rise in fault current, which in turn reduces the time it takes for the protective device to operate.

I think he needs to calculate it properly

 

[Engineer54]

Was wondering for the 10mm if the armour alone is enough for CPC or would need to carry a ajourning CPC? and the correct cable selection being used for the current capacity?

As far as using the armour for your CPC, ...i can confirm that a 4 core 10mm SWA cable has a CSA requirement of 22.6mm,to meet compliance. The actual CSA is 43mm so it does comply. If you decide to use a 4 core 16mm SWA cable, the CSA requirement is 36.1mm. The actual CSA on this 4 core is 49mm, so once again it complies...

In fact ALL cables 2, 3, and 4 core SWA cables of both PVC and XLPE insulation, will comply up to 95mm. Only then, do you need to check the tables for compliance....

 

[netblindpaul]

You can't use the 90 deg C current ratings, unless the accessories you are connecting to are also rated at 90 deg C, not many are.
Well in the domestic, small commercial, & small industrial situation.
Some of the larger kit may well be rated in excess of 105 deg C.
However, normal type A & B boards, socket outlets etc. are 70 Deg C.