To E-Stop or not to E-Stop? 1

[daKlone]

We are currently designing a power supply enclosure for external use. It will be powered from a 64A 230V 50Hz AC, which is both MCB and RCD protected. It will contain 4 x 3kW 28V DC power supplies. The enclosure will be IP65, and will be permenently fixed outside.

The 16th Edition IEE reg 463-01-01 states that 'a means of emergency switching shall be provided for every part of an installation which it may be necessary to cut off rapidly from the supply in order to prevent or remove danger'.

My question is simple (!) - am I required to fit an emergency stop to each of these enclosures? My gut feeling is yes, but I can't easily quantify the situation in which the e-stop would be required.

Help from anyone with knowledge/experience in this area would be appreciated.

Regards,
dK

 

[ScottyUK]

I'm in the UK, and my feeling would initially be no, it does not require an ESD, because suitable protection for the cabinet provided in the form of an MCB / RCD combination. It doesn't sound like a severe or catastrophic failure within the cabinet could occur without tripping one or both of your protective devices.

However, I would go on to say that if the load connected to the supply can give rise to danger, and that danger could be removed by tripping the power to the cabinet, then it may be necessary to fit an ESD. Can you expand on the nature of your load, as this will probably determine whether you need an ESD or not.

 

[daKlone]

Hi Scotty,

Thanks for the prompt reply!

Each of the PSUs are effectively generator replacements, suppling power to parked vehicles in place of an external generator.

Regards,
dK

 

[ScottyUK]

dK,

I think if you have correctly sized overcurrent protection on your PSU output, plus the MCB / RCD you describe on the mains input, that should be adequate. I don't see a requirement for an ESD based on what I understand of your application.

Be aware that some MCB's are not designed for DC duty, so if you choose to use MCB's on the output, choose carefully. ABB market DC rated MCBs in the UK, no doubt there are others. Personally I would use fuses on the output, with a DC rated switch.


regards,


Scotty

 

[jbartos]

Suggestion: The 28V DC power supply is not considered dangerous voltage level. However, the danger caused by 3kW power supply to a parked vehicle needs to be objectively evaluated, whether or not there are any regulations for the power supply to the parked vehicles.

 

[panelman]

door interlocked isolator on the mains?....available in red and yellow to use as E stops

mike

 

[uno]

daKlone


If the emergency stop is required for safety then sometimes it can be avoided by a safety work procedure. For instance if your maintenance/safety procedure calls for the Main supply to the panels to be switched off and padlocked and blocked for a switch-on by an authorised person, then a emergency stop may not be required .

I agree with scottyUK on the MCB/RCD to be adequate otherwise.

 

[RBE]

as panelman says an door isolator would meet 463 01 01

 

[Walden]

This is covered in UK IEE Regs section 537-03 and 537-04.
As I understand it, emergency stops are required when there is danger of mechanical damage or injury caused by a moving machine. Such as someone's hair being caught in an exposed rotating spindle on a lathe or along a conveyor where someone may get their sleeve trapped. Emergency stop push buttons may be connected into the control circuit of the motor starter. The other type of switch required is when mechanical maintenance is being carried out. Here, covers are removed to expose the inside of a machine and the machine must not be re-started inadvertently; so all the electrical supplies are isolated. This switch may be a local multi-pole switch: or a plug and socket (if below a certain rating). Section 463 is concerned with switching off the electrical supply at source in case of a major fault in the connected plant. Pressing the circuit breaker release button on a distribution board would be an example of compliance with this regulation.

 

[jbartos]

Suggestion: The similar content is in NFPA 79.
Visit

http://www.nfpa.org

 

[EEAutomEng]

To touch on what MartinPirrie said about e-stops connected to the motor starter control circuit...careful consideration must be taken when putting an e-stop in to the motor starter control circuit. It would take too many words to explain how it should work so here is link:

http://www.ab.com/catalogs/s114-ca001a-en-p.pdf

I find this catalog to have some useful examples when designing for safety. Pages 37 and 38 show some good examples. Don't get me wrong, I am not advocating the use of AB.