Disconnect for power or control

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hhsting

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NEC 2017 Section 426.50(A) disconnect does it disconnect snow melter control cables or does it disconnect snomelters power cables? Its confusing its under control and protection. Does anyone know?


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hhsting said:
NEC 2017 Section 426.50(A) disconnect does it disconnect snow melter control cables or does it disconnect snomelters power cables? Its confusing its under control and protection. Does anyone know?


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No one know or have any opinions?
 
It disconnects the power, just like pretty much every other disconnect in the NEC (I would say every other disconnect, but I am sure there is something, somewhere that wouldn't be that way; I certainly can't think of one off the top of my head). The first sentance of 426.50(A) states that "All fixed outdoor deicing and snow-melting equipment shall be provided with a means for simultaneous disconnection from all ungrounded conductors."
 
d0nut said:
It disconnects the power, just like pretty much every other disconnect in the NEC (I would say every other disconnect, but I am sure there is something, somewhere that wouldn't be that way; I certainly can't think of one off the top of my head). The first sentance of 426.50(A) states that "All fixed outdoor deicing and snow-melting equipment shall be provided with a means for simultaneous disconnection from all ungrounded conductors."
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I have snowmelter where it has relay panel. The 240V single phase power conductors for snowmelter go thru relay panel. The relays are powered by 120V. The relays have contactor which control the disconnect of power cables.

The disconnect i have disconnects the 120V relay power which opens snowmelter power cable contactor in relay panel

Contactors are controlled electrical so I see it as electric disconnect not a manual one that one would actually place between conductors. Would such a disconnect be compliant with 426.50(A) or not? See below

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hhsting said:
Contactors are controlled electrical so I see it as electric disconnect not a manual one that one would actually place between conductors. Would such a disconnect be compliant with 426.50(A) or not? See below

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I would say "not" and a disconnect is required ahead of the control panel, unless the breaker location qualifies.
 
LarryFine said:
I would say "not" and a disconnect is required ahead of the control panel, unless the breaker location qualifies.
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See below the snowmelter disconnect ahead of control panel and panelboard breaker feeding that control panel.

The red disconnect disconnects the control cable power which then disconnects the relay contactor for power of the snowmelter cable.

Looking at definition NEC 2017 section 100 of disconnecting means its a device. Definition of device would not electrical relay with contactor be considered device?

I am confused where in NEC 2017 it says this would not be acceptable form of disconnect?



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Possible 409.110 (3) would apply and control panel so marked.
 
hhsting said:
See below the snowmelter disconnect ahead of control panel and panelboard breaker feeding that control panel.

The red disconnect disconnects the control cable power which then disconnects the relay contactor for power of the snowmelter cable.

Looking at definition NEC 2017 section 100 of disconnecting means its a device. Definition of device would not electrical relay with contactor be considered device?

I am confused where in NEC 2017 it says this would not be acceptable form of disconnect?
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Your red item would disconnect only the 120V control circuit, it does nothing to disconnect the 240V power circuit, nor the 120V power on relay #1.

Disconnecting only the relay control circuit does nothing if the relay contacts are stuck in the 'closed' position. This is why NFPA70E, NFPA79, and OSHA require disconnects in the power circuit for LOTO purposes. The NEC requirements for lockable devices are usually based on being able to conform to these other standards.
 
jim dungar said:
Your red item would disconnect only the 120V control circuit, it does nothing to disconnect the 240V power circuit, nor the 120V power on relay #1.

Disconnecting only the relay control circuit does nothing if the relay contacts are stuck in the 'closed' position. This is why NFPA70E, NFPA79, and OSHA require disconnects in the power circuit for LOTO purposes. The NEC requirements for lockable devices are usually based on being able to conform to these other standards.
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+1. Nowhere that I know of allows a control device to function as a disconnect unless it can be physically opened manually and locked in that position. A contactor coil control circuit is NEVER a LO/TO safety device.
 
jim dungar said:
Your red item would disconnect only the 120V control circuit, it does nothing to disconnect the 240V power circuit, nor the 120V power on relay #1.

Disconnecting only the relay control circuit does nothing if the relay contacts are stuck in the 'closed' position. This is why NFPA70E, NFPA79, and OSHA require disconnects in the power circuit for LOTO purposes. The NEC requirements for lockable devices are usually based on being able to conform to these other standards.
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Not quite. The relay contactors are normally open. The 120V powers the relay so the contactors are closed which then powers the snow melter heat cables.

So when 120V disconnect ahead of the control panel is opened the power to relay is lost thus the contactors open and the power to the heat cable is off.

The 120V disconnect would be lockable open.

I dont follow your reason no where i see in NEC 2017 this is not recognized as disconnecting means.

I mean definition of disconnecting means Article 100 says device or group of devices. Definition of device Article 100 is electrical relay not considered a device? The relay, contactors and the 120V disconnect together are group of devices no thus disconnecting means?
 
hhsting said:
Not quite. The relay contactors are normally open. The 120V powers the relay so the contactors are closed which then powers the snow melter heat cables.

So when 120V disconnect ahead of the control panel is opened the power to relay is lost thus the contactors open and the power to the heat cable is off.
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I do not need to justify my position, do what ever you want.

But for your consideration:
The relay cannot disconnect the power if its contacts are welded shut or the mechanism is jammed in the closed position.
Does the relay have the ability to be locked open as the NEC requires?
 
hhsting said:
So when 120V disconnect ahead of the control panel is opened the power to relay is lost thus the contactors open and the power to the heat cable is off.
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That still does't cut power to the control unit.

By your logic, an A/C compressor should only require a disconnect on the 24v control circuit.
 
jim dungar said:
I do not need to justify my position, do what ever you want.

But for your consideration:
The relay cannot disconnect the power if its contacts are welded shut or the mechanism is jammed in the closed position.
Does the relay have the ability to be locked open as the NEC requires?
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Your thoughts are quite unusual. Lets say manual switch was place then the contacts of manual switch can get jammed you know then what? Lets now worry about person walking and piano falling too

In case of contactors yes the group of devices can be locked open thru the 120V disconnect if its lockable opened then contacts are locked open too
 
LarryFine said:
That still does't cut power to the control unit.

By your logic, an A/C compressor should only require a disconnect on the 24v control circuit.
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Their is one source of power to control unit 120V. The other 240V pass thru contactor it doesnt power the relay that 240V powers heat cable only. So when 120V disconnect is hit it will shut power to control unit
 
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hhsting said:
Their is one source of power to control unit 120V. The other 240V pass thru contactor it doesnt power the relay that 240V powers heat cable only. So when 120V disconnect is hit it will shut power to control unit
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It gets a red tag from me...when the code requires that power to equipment be disconnected, the disconnect itself must open the power circuit. Opening a control circuit and having the control system open the power NEVER counts as code required disconnect.
 
don_resqcapt19 said:
It gets a red tag from me...when the code requires that power to equipment be disconnected, the disconnect itself must open the power circuit. Opening a control circuit and having the control system open the power NEVER counts as code required disconnect.
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Where is that in the code? Code never says manual
 
jim answered it in post #11
Your reference is 426.50
among other things: simultaneous disconnection from all ungrounded conductors & The disconnecting means shall be of the indicating type and be capable of being locked in the open (off) position
 
augie47 said:
jim answered it in post #11
Your reference is 426.50
among other things: simultaneous disconnection from all ungrounded conductors & The disconnecting means shall be of the indicating type and be capable of being locked in the open (off) position
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Forgot about Jims something wrong the mechanism that can happen to manual disconnect the switch contactors jammed. If that was the concern NEC never states that to use manual disconnect

Wouldnt the relay have the capability of being locked open if the upstream disconnect has the capability of being locked open?
 
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