Adiabatic equation

[Engineer54]

Why not see if you can use the armour as the CPC?

There should be no problem using the armouring as a straight CPC, the problem comes if there is any bonding involved at these MCCB panels!!

 

[Spoon]

There should be no problem using the armouring as a straight CPC, the problem comes if there is any bonding involved at these MCCB panels!!

Very true Eng54 but the OP hasn't mentioned that additional bonding is required, so I thought that the armour should be OK for his purpose.

 

[Engineer54]

Unfortunately, most don't even consider the bonding side of things in the first place, so just because it hasn't been mentioned by the OP, doesn't mean it's not a consideration that should be taken into account....

 

[infinity]

There is no bonding required, i will be using armour as CPC and a 25mm fly lead to the board from gland (have 25mm in van to use up)

 

[Buzz-light-bulb]

There should be no problem using the armouring as a straight CPC, the problem comes if there is any bonding involved at these MCCB panels!![/QUOTE]

I am very interested as to why bonding would cause a problem.

 

[davesparks]

There should be no problem using the armouring as a straight CPC, the problem comes if there is any bonding involved at these MCCB panels!!

I am very interested as to why bonding would cause a problem.[/QUOTE]

Because it becomes very difficult to have armouring which complies with the requirements for a bonding conductor.

 

[Electric Yo]

Well if your ZS is accurate then a 10mm2 copper cpc will do the trick with a bit of headroom to spare.

 

[Buzz-light-bulb]

There should be no problem using the armouring as a straight CPC, the problem comes if there is any bonding involved at these MCCB panels!!

I am very interested as to why bonding would cause a problem.

Because it becomes very difficult to have armouring which complies with the requirements for a bonding conductor.[/QUOTE]

Please explain more, do you mean the reason is because bonding has to be bonded from the m.e.t ?? And not from the mccb panel

 

[infinity]

Can you show your calculations for 10mm please? Ive done it a few ways, including working out t instead of assuming 0.1 and I still get 16mm required

 

[davesparks]

Please explain more, do you mean the reason is because bonding has to be bonded from the m.e.t ?? And not from the mccb panel

For example if bonding was required to be 50mm copper at the intake then it would have to have a path back to the MET which is never less than 50mm copper.
Steel is 8 times less conductive than copper so to achieve this with steel armour the actual CSA of the armour would have to be 50x8 = 400sqmm of steel.

Or at least that is my understanding of it, I'd wait for the local earthing expert to share his knowledge before taking it as gospel though.

 

[D Skelton]

Or at least that is my understanding of it, I'd wait for the local earthing expert to share his knowledge before taking it as gospel though.

Where is D.W. Cockburn when you need him?!?

 

[Electric Yo]

Zs=0.04Ω
V= 230V

230/0.04= 5750A

-----------------

I=5750A
T= 0.025s (Read this from you post, also agrees with regs)
K=115


S = √((5750²)x0.025)
-----------------
115

S= 7.906 mm²

So with a 10mm² you will be oversized by 21%.

-----------------------------------------------

If you want to use the Steel armoured of the SWA:

I=5750A
t=0.025s
K=51 (assuming thermoplastic)

S = √((5750²)x0.025)
-----------------
51

S= 17.827 mm²

If you're thinking 'Jesus Christ that seems small' remember that the cpc only has to take this fault current for 0.025 seconds. And 21% is a nice amount of headroom, only if the result was borderline would I move up too the next size.

I presume you got the result:

S= 15.811mm² ????

That's because you used 0.1 as the value of 't' instead of 0.025. t is the actual disconnection time for your PFC (not maximum allowed or anything else). The actual disconnection time can be found by looking at the disconnect time curves in the reg, or better still from the manufacturers data sheet.

Hope that helps. =)

 

[polo1]

At last! Someone has actually provided what the OP was looking for

 

[Geordie Spark]

Where is D.W. Cockburn when you need him?!?

Swapping stories with Old Jag Lover the last I heard.