Do E Stops Need a manual reset or not

[TailSpin]

Hi All,

This is an issue with air handing units that have E stops fitted to stop the supply fan and main fan unit. At the moment on most AHU,s there is no manual reset on these units. So once the E stop has been activated the unit will re start when the stop is reset.

It seems that there is a lot of discussion on this type of question.

I know in the 17th reg : 537.4.2.6 at the bottom of the text it stats :

The release of an emergency switching device shall not be re-energize the relevant part of the installation.

Also are AHU's covered under machine law if so this is some text from it :

Once active operation of the emergency stop control has ceased following
a stop command, that command must be sustained by engagement of the
emergency stop device until that engagement is specifically overridden; it
must not be possible to engage the device without triggering a stop
command; it must be possible to disengage the device only by an
appropriate operation, and disengaging the device must not restart the
Machinery but only permit restarting.

Risk assessments and categories are also mentioned but I am not sure if this changes the out come.

Any Help on this would be appreciated.

Regards

Tail Spin

 

[silva.foxx]

I worked on AHUs back in the day and also recall the local e/stop, that would allow the fan to restart upon release! Scary. To think I used to change out drive belts with just this e/stop, as no local isolation.

You need to risk assess the situation really. In this day I would definitely have the e/stop circuit requiring reset and needing the AHU to be restarted also.

.

 

[jpmiff]

how do you reset the E stop?

 

[xraytek]

I am not familiar with AHU's but wonder if the fans are driven by contactors?
If they are, are the contactors monitored by the safety circuit via an N/C contact?
If it is then you can stick a N/O reset button in series with the N/C of the contactor.

Whether its required or not is all down to risk assessment, but if the reset button is a simple addition then no reason not to add one.

 

[TailSpin]

Thanks For all your replies.

I look after a lot of Air Handling Units all with E stops. They all have a mixture of contactors overloads,soft start or inverter control systems. On these AHU's very few have a manual re sets, so in other words when the stop is re energised the unit will just re start. This just seems wrong as I have known E stops to fail. So I was just trying to clarify if the manual re set is a must or not .

Regards

Tail Spin

 

[telectrix]

agree with previous posts. E/stops are Emergency Stops. Suppose some clown comes along and resets it. Nothing to do with IEE in my opinion, just common sense and safety. Restart of any machinery should only be undertaken by a competent person, once he/she deems it safe to do so.

 

[Guest123]

IMO it's always been a big no no. Releasing the EM stop should not result in that piece of equipment re-starting automatically, it must be physically re-started via another method.

All IMO.

 

[davelerave]

i think an additional key-start or similar is needed

not too familiar with them


not allowed anyhow for sure

 

[telectrix]

wouldn't like my lily whites in the workings if it were possible for somebody else to click a button and switch it on

 

[Guest123]

I believe Puwer98 would apply here also.

Puwer

 

[thepurple1]

Normally an emergency stop would have been pressed for a reason, the last thing that you want is for something to start atomically with out it being checked by a competent person

 

[TailSpin]

Hi Lenny

Not to familiar with Puwer98 is this again all part of the risk assessment process ? or is there a clear answer lurking in the regulations.

Regards

Tailspin

 

[Wazzajnr]

General consensus and a good rule of thumb is that if there is 1 estop local to 1 fan and it only controls that fan, it should be a twist or pull to release button that drops out the latch on the contactor. Therefore, the machine will not start until you press start again but you have to manually twist or pull the button to release.

If you have several fans or any other machine with multiple estops, then each e/stop should stop all parts of the machine. They should also be twist or pull release and there should be a separate button (Normally illuminated) to reset the estop relay. The buttons should be minimum of dual channel.

This is only a general rule of thumb. Yes, a risk assesment must be performed to decide where estops are required but there are very specific standards written describing exactly how they should operate.
The standard is BS EN 418 if i remember correctly.

Hope this helps

 

[TailSpin]

Thanks again for all your thoughts

Regards

Tailspin

 

[nickblake]

normally stop starts are installed in conjunction with contactors and stop start switched , i worked on one last week which had been wired incorrectly and would operate when the start button was pressed and stop when realeased even when the stop buttot had been pressed not good the only way round it was to install another small contactor so that the supplies were copmpletel controlled but the ES switches

 

[netblindpaul]

BS 7671 doffs its hat to BS EN 60204-1.
The release of an emergency stop button must not re-initate operation of the device in question full stop.
This is also a breach under PUWER98.
The fan motor can have a local e-stop, thus must act on the control system.
It should also have a local isolator to comply with BS7671.
The control voltages etc must comply with statutory legislation.
The e-stops must comply with PUWER98.
It is dubious whether it is acceptable for an e-stop to simply control one device in a system.
For example a machine e-stop would shut down the complete machine, thus an AHU e-stop should shut down the complete system connected to the AHU as this is the button of last resort!
As a parting shot, to be an e-stop under PUWER then MUST be latching end of.
The reset, prior to start, the illuminated reset button and the reference to BS EN 418 could be a red herring dependent upon the macinery in question and the design FMEA & RA carried out by the original designer, which the installer must comply with to ensure that they comply with law.

 

[xraytek]

I have just had a look for 2006/42/EC which are the latest statutory regulations for european machinery, and have found a copy here
Page 16-17 deals with emergency stops and states the following:

1.2.4.3 "Once active operation of the emergency stop device has ceased following a stop command, that command

must be sustained by engagement of the emergency stop device until that engagement is specifically overridden;
it must not be possible to engage the device without triggering a stop command; it must be possible
to disengage the device only by an appropriate operation, and disengaging the device must not restart the​

machinery but only permit restarting."

 

[Guest123]

disengaging the device must not restart the[/LEFT]
machinery but only permit restarting."

That seems to be the winning statement.