Isolator Or Not

[Martin]

I am fitting a TP board in a small tankhouse. One of the circuits is a pump set with a 2.2kW 3ph motor and a DOL starter. The board, starter, and motor are in close proximity. My question is would you fit a separate isolator or rely on isolation via the mcb for maintenance?

Regards

Martin

 

[northernspark]

I'd always fit an isolator clearly marked up with what it serves, I know it says in the BGB that you can use an mcb for isolation purposes but its something 98% of the sparks I know and work/have worked with never do 

 

[Evans Electric]

I agree with Northern  , in real life , only a sparks would look in the board for a means of isolation , anyone non electrical , working on the pumps would expect to see a nice red & yellow isolator adjacent to them.

 

[steptoe]

and the fact that stuff gets shuffled around in boards, and the labels never get changed,

but that never happens in real life, does it?

 

[apprentice87]

Well, I definitely would fit an isolator for several reasons. First off it makes things better for non electrical types, is easier to lock off too.

Secondly, what about the type of earthing?? I suppose it would be rare, but if it were TT you would have to isolate the neutral anyway, how you going to do that with an mcb? Thirdly, i never like relying on an mcb having had a shock in the past from supposedly "dead" neutrals. How you know that the neutral is not shared somewhere, or what if there is a neutral fault elsewhere and then your bit suddenly becomes live...

john...

 

[Martin]

Thanks guys for your thoughts, some valid points made so isolator it is. For the record the earthing is TNS, but I'm at a loss to understand what this has to do with a neutral, it would be an unusual 3 phase motor that needed one, but I do understand the thinking.

Regards

Martin

 

[Sidewinder]

Isolation for mechanical maintenance...

537.3 Switching off for mechanical maintenance
 
I would not like to rely on an MCB, noting that a DB could be in an area that is not "normally" accessible, and even could be under lock & key preventing isolation, thus an isolator external could well be required.
 
Finally 60204 & more to the point PUWER98 require the provision of isolation of ALL sources of energy, could an N conductor be a source of energy, yes is the answer, perhaps under fault conditions, but it can kill.
 
Once again there is more to this than meets the eye.

 

[northernspark]

Plenty of installs out there with unbalanced loads too so like its been said even if the circuit is isolated via an mcb there's still a possibilty there's current on the neneutral 

also when doing maintenance there's nothing worse than having to mess about looking for a point of isolation to carry out work on that equipment, it all adds time onto a job and in an environment where time is money and any downtime incurs serious costs the time saved not having to access a db etc to isolate a circuit is always a good thing