16th Edition - Isolation

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.

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.

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.

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).

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

snipped-for-privacy@medes.net

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.

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.

Hi again

A local isolator also provides a good position for disconection should the motor need to be removed for repair it is not acceptable in the uk, for cables to be left disconnected and loose even if they are taped up for any length of time even when they are switched off 1 meter away.

Martyn

snipped-for-privacy@medes.net

Relevant regs

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

NEC doesnt apply in UK.

sQuick..

According to the requirements of EN 60204-1:1997 Safety of machinery ? Electrical equipment of machines. When the equipment connected is a machine, it should have a supply disconnector (Isolator) fitted, to isolate the mains supply that meets the requirements EN 60947-3, category AC-23 B or have a Power CB suitable for isolation to EN 60947-2 as part of the machine. When it is required to provide a means of disconnecting a motor that forms part of a machine this isolator should also meet the above requirement. Therefore I would expect the same requirement to apply to the 16th Edition for electric motors.

BillB

Switching and isolation are two different things.

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

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

you are not actually saying you would work on a machine for mechanical purporses with just a stop button pushed in ?? even if you lock it off push buttons often have less that a 2mm contact gap and as for the regulations in the uk I have never had anyone say "lockout tagout" to me yet as far as I am concerned there is only one method of working and its called safe isolation which states that a minimum contact gap of 3mm must be achieved.

I know if i only provided a push button for isolation, other that emmergency situations and someone used it to isolate while working then I would be setting myself up for a spell in jail.

the only time you dont put an isolator within reach of the motor is when the machine has a incoming isolator that can be sucessfully locked off and even then i would be removing the supply cables for the item I was working on within the panel before working.

Martyn

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.

BillB

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

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.