swa on consumer unit

[moose man]

ifyou have to use swa if the consumer unt is more then 3mtr away frrom service head

on a tns system and a 80A incommer how do you get on if your exsisting tailes are 25mm and main earth is 16 mm as i have not come across this before i know to put you have to put switched fuse in but at @ 80A but discrimination between switched fuse and service fuse

all so how about sizeing 16mm 0r 25mm swa and do you use 3 core the 3rd core as the earth

to comply when the main earth is 16mm

i know it sounds a daft quiestion but i am just pondering on it thanks

moose man

 

[Revved Up Sparky]

If the load permits, I would be tempted to use a 60A switchfuse/ 63A MCB, using either a 2/ 3 core 16mm SWA or, if practicable 16mm singles in surface trunking. The 63A rating would give you discrimination from the 80A service fuse and using the SWA/ surface trunking should eliminate the need for RCD protection on the submain and thus provide discrimination for a 30mA dual RCD consumer unit. I don't see any problems with using a 2 core SWA as long as the CSA of the SWA works out at > 16mm and earth continuity is correctly installed (eg, metal consumer unit & switchfuse/ or earth straps from earth rings).

 

[moose man]

if work out without divesity the load = 80A i understand the need for earth rings as i have do this on a industrial scale

but never on a domestic with plastic enclosure when the cable as to pass threw a wall

 

[davetheglitz]

Try this

80AMCB MCBs - Protek Circuit Protection

XPLE 3C Cable d is good for 86A surface clipped according to TLC - so gland into a box and either feed through the exposed conductors direct (might be an idea to heat shrink an additional sheath) - or use a Henley.

Personally I don't think discrimination would be an issue. Pound to a penny the MCB would trip well before the 80A fuse - but either way I can't see there is a safety issue here.

 

[Sidewinder]

I personally avoid using the SWA as the only earth, too prone to damage to sheath and other issues from there.

 

[steptoe]

yep, throw in a bit of 3c 25mm SWA,

Ive done this pic before, but I'll post it again anyway.

 

[Electroglow]

Or what I do is use a bigger a box and put the Henley blocks in there then 25mm tails out all in stuffing glands

 

[moose man]

thanks for the pic steptoe its all down to expereance of this type of work being carried out as i have not done a lot this way in domestic way normaly service head next to cu on most ocasions

---------- Post Auto-Merged at 16:34 ---------- Previous post was made at 16:32 ----------

I personally avoid using the SWA as the only earth, too prone to damage to sheath and other issues from there.

same here sidewinder all ways order it with extra cores for the same reason

 

[PC Electrics]

I personally avoid using the SWA as the only earth, too prone to damage to sheath and other issues from there.

especially when it's a buried or outdoor cable. Even the slightest damage to the outer sheath will let water in to rot out the armour and, hey presto, no earth connection. If you conducted a DFMEA on such an install you'd have to give the severity a 10 which would require a redesign (ie add a cpc core).

I'm ok with it in indoor, surface mount, comm/ind though.

 

[Sidewinder]

Thing is PC how many sparks understand DFMEA's!

It is from our past so we have done this.

It is not taught as part of the training for an electrician these days, and years ago was not thought of to be taught.

It has sort of missed them out even though it is a valuable tool.

 

[steptoe]

but what is taught during training these days?

they just about have enough time to teach how to pass the exam,

5weeks clearly isnt long enough, needs to be 8 at least.!

 

[PC Electrics]

Yes, I agree. my apprentice is only in his second year, but I worry that the course will not teach him to design properly, utilising the usual tools....

As yet, he still doesn't know (from college) how to wire up a light circuit. He's never seen the wiring diagrams yet!!

 

[Robin Spark]

Or what I do is use a bigger a box and put the Henley blocks in there then 25mm tails out all in stuffing glands

Hopefully a plastic box and not metal as you might be introducing eddy currents by using individual stuffing glands on singles, thats why steptoe cut a slot so that both line and neutral are entering the same whole.

 

[a1]

He's never seen the wiring diagrams yet!!

There are some lovely ones that I have made, in the download area.

Is "DFMEA" = Diagnosis, Failure Modes and Effects Analysis ?

 

[Sidewinder]

Design Failure Modes & Effects Analysis

 

[wozz]

Could someone do a DFMEA and post it as I have never seen one?

 

[steptoe]

what for?

they are pretty much unique for each job,

ie, the design will not be the same for any 2 given jobs, will it?

failure rate in a high intense industrial environment will be much larger than in a used once a year spare room,,, etc...

 

[wozz]

the layout of the form and the risks and how a redesign has been decided on. Specific to the thread.

 

[Sidewinder]

wozz,

look here for an overview:

Failure mode and effects analysis - Wikipedia, the free encyclopedia

This is not quite exact, but, will give you an idea.

For design you would plug in the aspects of the design and how they could fail.

Too late now mate, to busy and too tired, as usual!

I will try to put something together but it will go on the end of a very long list I'm sorry.