240V Crk with one leg switched

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iwire said:
It's only safer if you don't know the rules right?

It seems you want others to exceed the rules (switch all poles) so that some can ignore the rules (not opening the disconnect, not checking for voltage)

I can't agree with that.
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No I don't want others to exceed the rules or ignore the rules, but I cant agree that having a constant energized conductor to anything is safer than not having it.

JAP>
 
I know the rules but accidents happen.

I might fall asleep with a fork in my hand, wake up, stretch out and stick it in a receptacle and get shocked.
None of which would happen if there wasn't any power at the receptacle to begin with.

By the way mine aren't tamper proof so don't go there..... :)

JAP>
 
Purely Resistive load

Purely Resistive load

A purely resistive load may have an open leg. Any inductive load may not have any open legs.
 
ZCBee said:
Okay, the training on the home and commercial side verses the industrial side is different from what I can make out from the conversation. My perspective is like this:

We have had to find ingenious means to keep personnel out of circuitry and here is why. My coworker has their production supervisor breathing down his or her respective neck to "make the numbers". The machine breaks just after the super chewed out my coworker. The coworker, fearful for her job, opens the control cabinet and starts pushing reset buttons and accidentally contacts a live circuit. She was just trying to do her job and all of the OSHA regulations in the world did not stop her from trying to keep her livelihood in tact and her supervisor happy. I therefore am ethically bound to do all in my power to make it human-nature proof as I can. And that sums up the training programs and engineering standards put in place becasue this type of incidence has happened enough times to warrant a $300 contactor.

Modern interlocks have been engineered to remove this as much as possible, for safety/personnel protection. But, human nature is to outsmart something in its way of achieving success or a goal. I leave this to everyone's contemplation becasue the code is about protecting life and property only.

This scenario can bleed over into the homeowner realm just as easily. Say the homeowner hires a handy service who has some electrical training. The "some" part is the key element in this version. How the heck do you control the qualified personnel in a homeowner situation?

I have not seen a 2-pole mcc setup used for 3 phase circuits. My plant goes back to the mid 80's for some of its equipment and have not come across this usage. But, I bet that this would be a "Qualified Personnel" situation due to a 277V shock potential.
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You may have safety policy that requires more then the NEC requires, this is design issues not code issues. The situation of opening a cabinet and going through reset buttons - they make reset buttons that pass through the door. Sometimes the door can't be opened unless the disconnect for supply power is in off position.

As mentioned a disconnect must open all ungrounded conductors of the circuit, a controller only needs to open what is necessary to perform the desired control function. If you have a device that qualifies as both disconnect and controller then it must open all ungrounded conductors. This doesn't really even change between residential and non residential applications NEC wise.

ZCBee said:
A purely resistive load may have an open leg. Any inductive load may not have any open legs.
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Where are you going with that statement?
 
jap said:
No I don't want others to exceed the rules or ignore the rules, but I cant agree that having a constant energized conductor to anything is safer than not having it.

JAP>
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It is like saying having a live receptacle is dangerous.

It will do no harm unless you remove the cover and stick your fingers in where they don't belong.
 
iwire said:
It is like saying having a live receptacle is dangerous.

It will do no harm unless you remove the cover and stick your fingers in where they don't belong.
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If you can troubleshoot controls with the power off , I'll have to admit your a better electrician than I am.

JAP>
 
Automatic controls are not a switch from code point of view. The circuit is considered live and subject to energize at anytime.

Also, not all 240v systems are the same. You're not supposed to disconnect the grounded conductor on a corner ground delta system
 
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Electric-Light said:
Automatic controls are not a switch from code point of view. The circuit is considered live and subject to energize at anytime.

Also, not all 240v systems are the same. You're not supposed to disconnect the grounded conductor on a corner ground delta system
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You are not allowed to disconnect the grounded conductor unless your switch or OCPD also disconnects all ungrounded conductors at the same time.

Which for a corner grounded delta comes down to this: If you disconnect only two out of the three wires, the grounded conductor cannot be one of the two.
 
I recently came across the same issue with a residential pool sweep system. A timer was used that had 3 independantly controlled single pole contacts. It was used to control 2 230v pumps and the heater circuit. Hence, the pump and sweep motors have 1 hot leg when not running. To me, it's a very scary thought that a poorly trained pool guy will try to change the motor without turning off the breaker.

I highly recommended to the customer that we fix the issue by adding an additional controller
 
So here is the option for those who think a sp t-stat is dangerous, Write a proposal to change the code ruling or use a dp t-stat as Bob suggested and as I would do also. A disconnect is required so the DP t-stat with an off position is the easy way out IMO.
 
electricguy61 said:
I recently came across the same issue with a residential pool sweep system. A timer was used that had 3 independantly controlled single pole contacts. It was used to control 2 230v pumps and the heater circuit. Hence, the pump and sweep motors have 1 hot leg when not running. To me, it's a very scary thought that a poorly trained pool guy will try to change the motor without turning off the breaker.

I highly recommended to the customer that we fix the issue by adding an additional controller
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The poorly trained pool guy needs to learn to use the disconnecting means - that is why we put them there, and doesn't matter if it were only a 120 volt circuit, it still needs to be used.
 
Electric-Light said:
Automatic controls are not a switch from code point of view. The circuit is considered live and subject to energize at anytime.

Also, not all 240v systems are the same. You're not supposed to disconnect the grounded conductor on a corner ground delta system
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Who would?

Jap>
 
Dennis Alwon said:
So here is the option for those who think a sp t-stat is dangerous, Write a proposal to change the code ruling or use a dp t-stat as Bob suggested and as I would do also. A disconnect is required so the DP t-stat with an off position is the easy way out IMO.
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easy and breaks both legs so that is a good suggestion.

JAP
 
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