Requirement of local isolators for 3 phase motors on plant

[pepparz]

eng is a big boy, i'm sure he can stick up for himself

 

[Engineer54]

Really, ...think you need to read the thing yourself, ...As a qualified Engineer can alter anything in those regulations, provided they can prove that any such changes will at least equal or exceed that stated in BS 7671!! That's NEVER too difficult to achieve!!

As i'm exceeding the crap given in BS 7671, you are as usual, talking about things you have little understanding of!! In fact, Stick to advising about tieing new cables to existing fixed cables, you seem to know all about that!!

 

[pepparz]

eng knows his field, of course he does. but god help anyone who doesnt share his view.

- - - Updated - - -

his last post cements what i have just said.

 

[dazza1981]

Another bid brave book reader who grows big nuts behind his computer lol
People like you turn peoples threads into a (look how clever i am) joke and offer no good advice what so ever!!!

 

[pepparz]

not hiding behind a computer, its just that this is the only way to communicate on the forum.unless theres another way ur not telling me?

 

[Spoon]

Anyhow.... back to the question.
My opinion:
First: The title of the thread 'Requirement of local isolators for 3 phase motors on plant.' There is no requirement for 'local' isolation.
Next: This 'lockable emergency stop push button to kill the control circuit.' As mentioned in post 4. This is not classed as isolation.
For 'Guidance on the selection of protective, isolation & switching devices' see Table 53.4 (page 149 BGB)

 

[snowhead]

I don't know anyone who would rely on an EM stop for local isolation even for changing drive belts.

Fitting an EM stop would be pointless.

 

[pepparz]

no its not allowed (according to the regs). plus all line conductors to the machine should be isolated when isolation is required.

 

[D Skelton]

Lockable 'local' isolation is not a technical requirement however it would be prudent to install it for any control cabinet, motor control center, TP socket outlet or starter. Isolation will be seperate to any safety circuit so anyone considering e-stops for isolation really needs to rethink their methods!

'Local' isolation is less about safety, more about maintainability.

 

[Monty2010]

Thank you all for your feedback and input. My general feeling on this matter is that I am much happier to have a local isolator so that I know the system is safe and secure when I or any other person needs to work on any plant. The view of no isolators is a conflicting view between me and another electrical contractor on this job. To me the issue of cost has never been a problem as the customer is paying and the isolators have been priced in to an accepted quote. I just wanted to know the long and short of it.

I also disagree greed withh is views of isolating a control circuit as this provides no electrical isolation from the motor other than reliant that the contractor does not close or is pushed in. The plant is elevators, screw conveyors and seed dressers, all machinery that is unforgiving if limbs are inserted.

i will be installing isolators but I will obviously not be quoting regs but safety from a personal risk assessment in my argument when it continues with the other contractor.

cheers

 

[netblindpaul]

You need to look further than BS7671 as this may be irrelevant to motor controls like this remember check the exclusions from scope.

In the UK there will be statute law to consider, forget BS7671.

 

[TerryB]

I know that to add this is very late but just in case someone is trying to find out what to do then........LOOKING AT ELECTRICAL REGULATIONS IS THE WRONG PLACE; LOOK AT HEALTH AND SAFETY.
Quote "Where maintenance requires that normal guarding is removed, or access is required inside existing guarding, then additional measures are needed to prevent danger from the mechanical, electrical and other hazards"....... "The basic rules, however, are that there should be isolation from the power source (usually, but not exclusively, electrical energy), the isolator should be locked in position (for example by a padlock), and a sign should be used to indicate that maintenance work is in progress. Isolation requires use of devices that are specifically designed for this purpose; not devices such as key-lockable emergency stops or other types of switches that may be fitted to the machine".
One point that has not been mentioned is size /rating of the isolators. If the rating is less than the contacts can safely break when some one switches the motor on or off whilst on full load or full starting current you will need to have an isolator that breaks the control circuit before breaking the power circuit (early brake late make contacts) and the opposite for when you switch the isolator back on. This also means you have to run wiring for the control circuit to the isolator as well as the power cable. And no just running the control circuit through the isolator is not sufficient.