Emergency Power Shutdown for Boilers

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elec_eng

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Can a control panel to the boiler used as a disconnect mean for an emergency power shutdown? Normally, I would provide either a shunt-trip cb or contactors for this, but the boiler manufactuer is saying they can use their contactors in the control panel to shut off their equipment instead of disconnect the power supply.

I thought I can't use a control panel as a disconnecting mean. Can you provide me a code reference whether a equipment control panel can be used as a disconnecting mean or not? I am having a hard time finding this. Thanks.
 
I think we can consider an 'emergency power shutdown' to be different from a 'disconnecting means. The former might merely need to stop the equipment or process to simply stop, while the latter would need to put the equipment into a deenergized state to allow it to be worked on.
 
Em power shutdowns

Em power shutdowns

elec_eng said:
Can a control panel to the boiler used as a disconnect mean for an emergency power shutdown? Normally, I would provide either a shunt-trip cb or contactors for this, but the boiler manufactuer is saying they can use their contactors in the control panel to shut off their equipment instead of disconnect the power supply.

I thought I can't use a control panel as a disconnecting mean. Can you provide me a code reference whether a equipment control panel can be used as a disconnecting mean or not? I am having a hard time finding this. Thanks.
Click to expand...

I have installed numerous em shutdowns for boilers usually breakglass stations which are always located outside of the room that the boiler is in and have been designed by the engineers who drew the blueprints they break control voltage just past the xfomer and fuse on the control curcuit. Hello everyone the cow is back try not to pummell me as I am trying to brush up on my code I am not an engineer just trying to share my experience.
 
Volta said:
I think we can consider an 'emergency power shutdown' to be different from a 'disconnecting means. The former might merely need to stop the equipment or process to simply stop, while the latter would need to put the equipment into a deenergized state to allow it to be worked on.
Click to expand...

Let me rephrase it. Can a control panel be used as a disconnecting mean? If not, which code section prohibits this?
 
quogueelectric said:
I have installed numerous em shutdowns for boilers usually breakglass stations which are always located outside of the room that the boiler is in and have been designed by the engineers who drew the blueprints they break control voltage just past the xfomer and fuse on the control curcuit. Hello everyone the cow is back try not to pummell me as I am trying to brush up on my code I am not an engineer just trying to share my experience.
Click to expand...

Thanks for sharing your experience with me. However, according to ASME CSD-1, the em shutdown is supposed disconnect all power supply to the controller. I am not sure breaking the control voltage meets that requirement. I would think a disconnecting mean should be required before the controller but I can't find a referece that prohibits the control panel as a disconnecting mean. Any idea?
 
Is the switch being used as a disconnect switching the control circuit or is it switching the main incoming power and by operating this switch you also open power supplying control circuit and it happens to be located in the control panel?

That is a disconnect but is not the same thing as an emergency stop button.

The title of thread indicates emergency stop button yet your topic of discussion is disconnecting means, I think this has led to some confusion in the replies so far.
 
From NFPA79:2007: (Voluntary Standard for Industrial Equipment)
9.2.2
Category 0 Stop: Uncontrolled, remove all power immediately to machine actuators.
Category 1 Stop: Controlled, bring equipment to a halt then remove all power to machine actuators.
Category 2 Stop: Bring equipment to a halt, do not remove power to machine actuators.

9.2.5.4.2.2 Emergency switching off shall be a category 0 stop initiated by a single human action except where category 0 can't be tolerated.

9.2.5.4.1.3 Emergency stops shall be either category 0 or category 1 determined by risk analysis.

10.7.4 The disconnecting means may be used as an emergency stop providing it also passes the requirements and marking for an Estop.

10.8.5 The disconnecting means may be used as an emergency switching off device providing it also passes the requirements and marking for one.
 
kwired said:
Is the switch being used as a disconnect switching the control circuit or is it switching the main incoming power and by operating this switch you also open power supplying control circuit and it happens to be located in the control panel?

That is a disconnect but is not the same thing as an emergency stop button.

The title of thread indicates emergency stop button yet your topic of discussion is disconnecting means, I think this has led to some confusion in the replies so far.
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Kwired,

Sorry for the confusion. I guess I have two questions. Let me try again

I need to shutdown the power supply to the boiler by activating the remote emergency stop button. Currently, a remote emergency stop button is used to break the control circuit in the control panel, not the power supply to the control panel.

So my first question is can breaking the control circuit meet the requirement of power shutdown?

My second question really arose from the first question but I guess it is not really related to the topic. I think this is what confused everyone. The question is can a control panel be served as a disconnecting mean by breaking the control circuit? If not, which code section prohibits this?
 
Last edited:
pfalcon said:
From NFPA79:2007: (Voluntary Standard for Industrial Equipment)
9.2.2
Category 0 Stop: Uncontrolled, remove all power immediately to machine actuators.
Category 1 Stop: Controlled, bring equipment to a halt then remove all power to machine actuators.
Category 2 Stop: Bring equipment to a halt, do not remove power to machine actuators.

9.2.5.4.2.2 Emergency switching off shall be a category 0 stop initiated by a single human action except where category 0 can't be tolerated.

9.2.5.4.1.3 Emergency stops shall be either category 0 or category 1 determined by risk analysis.

10.7.4 The disconnecting means may be used as an emergency stop providing it also passes the requirements and marking for an Estop.

10.8.5 The disconnecting means may be used as an emergency switching off device providing it also passes the requirements and marking for one.
Click to expand...

This kind of explain what I am trying to ask. A disconnecting mean can be used as an E-stop but can a breaking control circuit used as a disconnecting mean?
 
Without code delving:
A disconnecting means must physically separate all upstream ungrounded lines from all downstream ungrounded lines.
The disconnecting means must be capable of lockout.
The device must be listed as a disconnecting means.

Very few Estops qualify. I would dare to say if it's an Estop that qualifies then it's probably sold as a disconnect and not an Estop.

In general, you can wire control circuits such that they perform in an almost perfect imitation of a disconnect and yet they won't qualify. You will still have to go find the REAL disconnect and lockout there.

That said, a well-wired safety control circuit can provide almost all the protection afforded by an actual disconnect including the ability to lockout the machine. But it still has to be listed for the purpose which means using an actual lockable disconnect.
 
A few boilers I have done required a EMG fuel cut off switch/button but not the circulating pumps, this allowed the water to keep cooling after the fuel has been shut off, from what I have been told over the years is if you shut everything down the water in the boilers can continue to rise in temp and if close to the limit of the boilers can cause a failure of the boiler.

A disconnect is only required for maintenance purposes.
 
Good point. So risk analysis might lead to the Estop function immediately affecting fuel, motion, etc but leaving the circulating pumps to run until the temperature dropped (Category 1 Stop). The disconnect should still be present in case the boiler ruptures and a Category 0 Stop is required.

Just maybe
 
elec_eng said:
Let me rephrase it. Can a control panel be used as a disconnecting mean? If not, which code section prohibits this?
Click to expand...

The disconnecting means can certainly be part of the control panel, assuming whatever requirements for a disconnecting means (such as in sight and lockable) are met.
 
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