16th Edition - Isolation

[BIGEYE]

There is a 16th edition requirement that a means of isolation must be
provided on electric motors to allow isolation of the equipment when
mechanical maintenance is to be carried out.
Is there any maximum/minimum distance as to how close to the drives the
isolators need to be?

A new installation is underway at one of our works, the design contractors
'overlooked' the requirement for isolators at the motors. They have asked if
the installation can go ahead without local isolators, as the drives can be
isolated on the MCC about 30 metres away and out of sight. There request is
based on cost, I think that is why they 'overlooked' this in the first
place.
TIA

 

[SQLit]

There is a 16th edition requirement that a means of isolation must be
provided on electric motors to allow isolation of the equipment when
mechanical maintenance is to be carried out.
Is there any maximum/minimum distance as to how close to the drives the
isolators need to be?

A new installation is underway at one of our works, the design contractors
'overlooked' the requirement for isolators at the motors. They have asked if
the installation can go ahead without local isolators, as the drives can be
isolated on the MCC about 30 metres away and out of sight. There request is
based on cost, I think that is why they 'overlooked' this in the first
place.
TIA

A local disconnect has been in the NEC for years ( at least 20 that I know
of)

Your description "out of sight and 30 meters" is not acceptable to the NEC.

Come on now just how hard is it to put a red mushroom button and run 2 wires
back to the controller.

Because of "lock out tag out" interpretations I always go with a lockable
mushroom.

 

[BIGEYE]

A local disconnect has been in the NEC for years ( at least 20 that I know
of)

Your description "out of sight and 30 meters" is not acceptable to the
NEC.

Come on now just how hard is it to put a red mushroom button and run 2
wires
back to the controller.

Because of "lock out tag out" interpretations I always go with a lockable
mushroom.

It is isolation I am asking about, where isolating the three phase power
circuit is required. Isolation of the control circuit by emergency stop
button may not be sufficient. An emergency stop or stop button is just as
the name implies, for stopping a machine in operation. Not for isolation
purposes.

 

[BIGEYE]

A "red mushroom button and two wires" is not a disconnect.It is a stop
button.A disconnect is a three phase splitter or rotary switch which
physically disconnects the mains from the motor/starter and must be
capable of being locked.I`m not sure about the distance from the motor
it has to be but it would be bad practice to have it after the
contactor.
regards,mark.

No - good practice. The MCC has an isolator already - usual the first
component in the MCC cubicle. The local isolator is in addition to this and
is before the power cable enters the motor. The isolator must be capable of
on-load disconnection, or if it is an off-load isolator, then it needs to be
fitted with aux. contacts that break before main contacts. The control
circuit is wired to these so that the contactor will drop out before the
local isolator breaks.
The purpose is for locally isolating a machine so that maintenance can be
carried out on the machine. Of course, it is also needs to have padlocking
facilities.

 

[Andrew Gabriel]

There is a 16th edition requirement that a means of isolation must be
provided on electric motors to allow isolation of the equipment when
mechanical maintenance is to be carried out.
Is there any maximum/minimum distance as to how close to the drives the
isolators need to be?

No.

However, unless the isolator is near enough to be under the sole
control of the maintenance person, it must be of a type which can
be locked in the OFF position with a padlock supplied by the
maintenance person, so they can be sure it remains locked off
and no one else will have a key to remove the lock.

I would suggest provision of a lockable isolator even if it is
positioned next to the appliance.

A new installation is underway at one of our works, the design contractors
'overlooked' the requirement for isolators at the motors. They have asked if
the installation can go ahead without local isolators, as the drives can be
isolated on the MCC about 30 metres away and out of sight. There request is
based on cost, I think that is why they 'overlooked' this in the first
place.

That's fine providing it is a proper means of isolation (i.e.
including neutral conductor isolation, not just an MCB disconnecting
the phase conductor) and it meets the locking requirements above.
Most industrial MCB's will meet the locking requirement (you will
see a small hole in the toggle and mounting through which a special
multi-lockable plate can be attached, allowing up to 6 or 8 separate
electricians to attach their padlocks to keep the MCB locked off),
but won't meet the isolation requirement unless they switch the
neutral (or there is no neutral connection to the appliance).

 

[BIGEYE]

A local isolator for the purporse of maintenance or service must be
located within 1 metre of the equipment to be isolated further more
weather or not it can be viewed it must be of locable type and break
all conductors with the exeption of earth, if this is as you suggest a
motor isolation must also be provided for thermistors if they are
present, therefore it is advisable to have one isolator with as many
auxillaries as is required to break all circuits including as
suggested to interupt the motor contactor/s. an emmergency stop button
is very much somthing to be avoided as this does not break the actual
circuit and could damage the drive unit,if pressed during startup and
the drive unit for the motor has thyristor's within then the sudden
rush of energy for the colapsing motor field will almost definatly
cause them to short out -this will cost you a fortune to repair Hench
stay clear of stop buttons whenever possible.

Martyn

[email protected]

Thanks for the replies. However, my interpretation of the reg. goes along
with Andrew's reply. In practice however, we do as Martyn says.
Everyone at work tells me that there should be an isolator in close
proximity to the drive, but I cant find any reference to confirm that a
local isolator MUST be provided. Isolator being as you describe, breaking
the phase conductors.
I have found a reference to these regs stating that IF a local isolator is
provided for mechanical maintenance, it must be positioned in close
proximity to the equipment so that it can be easily operated without
stretching or having to reach over equipment.

 

[SQLit]

It is isolation I am asking about, where isolating the three phase power
circuit is required. Isolation of the control circuit by emergency stop
button may not be sufficient. An emergency stop or stop button is just as
the name implies, for stopping a machine in operation. Not for isolation
purposes.

We use "E" stops on all of our 5 KV motors cause you can not see the
disconnects from the their location. A lock on the disconnect at the starter
and one on the "E" stop will prevent any starting of the equipment. There
is not enough room for mounting a "isolator" at the motor for 5 kv.


Unless I do not understand, isolation is a situation were the equipment can
not start. The above does solves the issue for us, the insurance company
and the OSHA guy that visits every so often.

 

[andicee]

Thanks for the replies. However, my interpretation of the reg. goes along
with Andrew's reply. In practice however, we do as Martyn says.
Everyone at work tells me that there should be an isolator in close
proximity to the drive, but I cant find any reference to confirm that a
local isolator MUST be provided. Isolator being as you describe, breaking
the phase conductors.
I have found a reference to these regs stating that IF a local isolator is
provided for mechanical maintenance, it must be positioned in close
proximity to the equipment so that it can be easily operated without
stretching or having to reach over equipment.

Relevant regs

131-14-01

131-14-02 Every fixed electric motor shall be provided with an efficient
means of switching off, READILY ACCESSIBLE, easily operated and so placed as
to prevent danger.

I'd say the above implies that the point of isolation should be within 1
metre. The way I've always done it anyway! This may or not be relevant but
if you installed a dso underneath a kitchen worktop, for a dishwasher/
washing machine for example, you are required to control that dso with a
switched fused spur ABOVE the worktop. If this applies to domestic
installations.......

Look also at

476-01 and 476-02

 

[sQuick]

A local disconnect has been in the NEC for years ( at least 20 that I know
of)

Your description "out of sight and 30 meters" is not acceptable to the
NEC.

Come on now just how hard is it to put a red mushroom button and run 2
wires
back to the controller.

Because of "lock out tag out" interpretations I always go with a lockable
mushroom.

NEC doesnt apply in UK.

sQuick..

 

[daestrom]

Relevant regs

131-14-01

131-14-02 Every fixed electric motor shall be provided with an efficient
means of switching off, READILY ACCESSIBLE, easily operated and so placed
as to prevent danger.

For *MECHANICAL* maintenance, there must be a local stop button that is
lockable. This is not an *isolation*, nor does it protect from electrical
work.

A lockable breaker/disconnect located on the MCC is used for *ELECTRICAL*
maintenance. And it must disconnect all current-carrying conductors
(including neutral if used). It does *not* need to be within one meter of
the equipment.

In industrial situations, the typical installation will include lockable
breakers/cubicles for electrical work and a local 'emergency stop'
pushbutton that interrupts the control circuits for mechanical work. But
most lockout/tagouts we hang always include locking the breaker open, even
if just doing mechanical work.

daestrom

 

[Andrew Gabriel]

For *MECHANICAL* maintenance, there must be a local stop button that is
lockable. This is not an *isolation*, nor does it protect from electrical
work.

I suspect you are talking about a different country.
Otherwise please cite the relevant 16th Edition regulation.

 

[daestrom]

I have been designing and servicing various types of machines since 1963
and
would never every consider working on any machine, without it having
having
an isolator. Every circuit I have designed for the last 20 years have had
an
isolator as specified by EN 60240.

Do you have isolators locally installed for each 4160V motor? Do you have
isolators for 2500 hp motors? Even 250 hp? We use locks on the breaker/MCC
to lockout/tagout motors for work. But the US code still requires local
'stop' buttons that are lockable.

After lockout/tagout of the supply breaker and circuits, lifting the motor
leads on a 2500 hp motor, just so you can replace the pump seal would be
silly. (have to lock/tag the breaker, it's the 'motor starter' and can be
manually closed).

daestrom

 

[Andrew Gabriel]

Do you have isolators locally installed for each 4160V motor? Do you have
isolators for 2500 hp motors? Even 250 hp? We use locks on the breaker/MCC
to lockout/tagout motors for work. But the US code still requires local
'stop' buttons that are lockable.

In UK, positioning of Emergency Stop buttons is a matter for the
Health and Safety regulations, not the 16th Edition (wiring regs).

However, an E-stop button does not count as an isolator for
maintenence purposes -- it might not actually isolate anything,
e.g. in some cases, it may provide powered breaking.
Furthermore, any lock on it belongs to the wrong party to be used
as a lockout, i.e. there might be other keys on the premises.
A safety lockout must be done using the electrician's own lock
and key (i.e. padlock) so the electrician can be sure no one
else on the premises has another key.

 

[daestrom]

In UK, positioning of Emergency Stop buttons is a matter for the
Health and Safety regulations, not the 16th Edition (wiring regs).

However, an E-stop button does not count as an isolator for
maintenence purposes -- it might not actually isolate anything,
e.g. in some cases, it may provide powered breaking.
Furthermore, any lock on it belongs to the wrong party to be used
as a lockout, i.e. there might be other keys on the premises.
A safety lockout must be done using the electrician's own lock
and key (i.e. padlock) so the electrician can be sure no one
else on the premises has another key.

Here in the US, we have E-stop buttons that take a padlock. So the workman
can use their lock on it.

daestrom

 

[daestrom]

May be silliy it may even take you a while and it may save your life!
but i suppose it is your life.

Sometimes a job like that might take six to eight hours, just 'lifting the
leads'. Pretty extraordinary steps. Some folks I know take the stance of
opening and removing the breaker from the cubicle. Problem with *that*
approach is it doesn't stop someone from installing another breaker from
another cubicle by mistake. They have to rely on the tagout hanging on the
cubicle door (the locking mechanism comes out with the breaker).

daestrom

 

[daestrom]

NFPA 79 requires all machines to have an isolator that can be locked off.

I agree. That can be met with a circuit breaker that can be locked open, or
can accept a locking device that in turn takes a padlock. I was commenting
on the practice of *also* lifting leads. With large machines, lifting leads
can be a difficult task. As I said, some folks take the approach of
racking-out/removing the circuit breaker to 'lift the leads'. But doing so
also removes the locking mechanism, so I think the protection that such
actions affords is dubious.

Our lockout/tagout program allows the use of tags only to prevent operation
that would damage equipment, but if personnel safety is involved, both locks
and tags are required. We've been through this with a host of outside
agencies, and all have agreed that our practices are acceptable for both
NFPA and OSHA.

daestrom