NEC on 'life' of electrical equipments

[T.M.Haja Sahib]

Hi,I have two questions.

1)Does NEC say anything (by reference) on the 'life' of electrical equipments from the safety point of view ?

2)Does provision of Stand by increase the 'life' of an electrical equipment?

Thanks.

 

[jim dungar]

The NEC does not directly address the 'life' of electrical equipment. As long as the equipment continues to perform its job, the NEC is happy. But, 110.3 says to use equipment per its instructions and most of them include something about maintenance.

OSHA and NFPA70E do both require regular maintenance.


Stand-by mode may extend the life of some equipment because it is not exposed to as much heat, however some equipment (i.e. breakers) have moving parts that will tend to seize if not operated regularly.

 

[Jon456]

however some equipment (i.e. breakers) have moving parts that will tend to seize if not operated regularly.

Hmmm... should individual breakers be "exercised" by flipping them off/on every so often?

 

[T.M.Haja Sahib]

Thanks for reply.The Government departments in some countries assign a 'rated life' to every electrical equipment under their control and dispose of the equipments at the end of the 'rated life',irrespective of whether the equipment is provided with a stand-by and operated alternatively in a regular manner or not.This may be good for safety,given poor maintenance.But this leads to a wastage of revenue.I do not know the procedure followed by American Government in this regard.

The NEC does not directly address the 'life' of electrical equipment. As long as the equipment continues to perform its job, the NEC is happy. But, 110.3 says to use equipment per its instructions and most of them include something about maintenance.

OSHA and NFPA70E do both require regular maintenance.


Stand-by mode may extend the life of some equipment because it is not exposed to as much heat, however some equipment (i.e. breakers) have moving parts that will tend to seize if not operated regularly.

 

[jumper]

I think Jim is talking about the big stuff. I seriously doubt the small stuff is excersized on a regular basis and only when turned off or tripped.

 

[T.M.Haja Sahib]

If the breaker is not exercised regularly,its becoming a hazard due to seizure of its contacts necessitating its replacement may not be known!

Hmmm... should individual breakers be "exercised" by flipping them off/on every so often?

 

[jumper]

If the breaker is not exercised regularly,its becoming a hazard due to seizure of its contacts necessitating its replacement may not be known!

Here you go T.M. I found this for you.

http://www.usbr.gov/power/data/fist/fist3_16/fist3-16.pdf

 

[weressl]

If the breaker is not exercised regularly,its becoming a hazard due to seizure of its contacts necessitating its replacement may not be known!

Most of the molded case circuit breakers do not have replaceable contacts. Large MV system breakers use vacuum contacts and contact resistance measurements will answer the "health" questions. The mechanical exercise is to assure that the actuating mechanism is not bound up but moves within the acceptable mechanical resistance limits.

With the growing sophistication of electrical equipment the useful life of those will be more limited by the obsolescence of electronic components. That will be even more pronounced with the smart grid components.

 

[weressl]

Here you go T.M. I found this for you.

http://www.usbr.gov/power/data/fist/fist3_16/fist3-16.pdf

This is more encompassing:
[h=1]NFPA 70B: Recommended Practice for Electrical Equipment Maintenance[/h]
Google for links....

 

[T.M.Haja Sahib]

Here you speak of 'Economic life' of an electrical equipment,whereas what I requested to know is how to show by calculation that the 'rated life' of an electrical equipment,say an air-conditioner, being used by Accountants for claiming Tax Relief and being conceptual and though not real, increases on provision of a stand-by to it.Thanks.

With the growing sophistication of electrical equipment the useful life of those will be more limited by the obsolescence of electronic components. That will be even more pronounced with the smart grid components.

 

[T.M.Haja Sahib]

But the breaker must be electrically exercised regularly by pressing the trip button.If it does not trip,it should be replaced ( molded case circuit breakers).

Most of the molded case circuit breakers do not have replaceable contacts. Large MV system breakers use vacuum contacts and contact resistance measurements will answer the "health" questions. The mechanical exercise is to assure that the actuating mechanism is not bound up but moves within the acceptable mechanical resistance limits.

 

[petersonra]

But the breaker must be electrically exercised regularly by pressing the trip button.If it does not trip,it should be replaced ( molded case circuit breakers).

Do most MCBs have trip buttons? The only ones I recall seeing that way were larger frame sizes, and I think they were all electronic breakers.

Most places would get seriously offended if those breakers were turned off on any regular basis.

OTOH, I am not sure I ever looked that closely.

 

[weressl]

But the breaker must be electrically exercised regularly by pressing the trip button.If it does not trip,it should be replaced ( molded case circuit breakers).

Most of the molded case circuit breakers do not have replaceable contacts. Large MV system breakers use vacuum contacts and contact resistance measurements will answer the "health" questions. The mechanical exercise is to assure that the actuating mechanism is not bound up but moves within the acceptable mechanical resistance limits.

As I've tried to explain it earlier, the manufacturer recommends the periodic, MECHANICAL excercise of the breakers.

 

[weressl]

Here you speak of 'Economic life' of an electrical equipment,whereas what I requested to know is how to show by calculation that the 'rated life' of an electrical equipment,say an air-conditioner, being used by Accountants for claiming Tax Relief and being conceptual and though not real, increases on provision of a stand-by to it.Thanks.

It is not an economical life alone, it is obsolescence, which means both technological unsustainability and the uncontrolled cost escalation of repair. At the end it is always abot cost and indeed you were requesting cost data. What you're asking can not be calculated because the actual service is hardly determinable with any accuracy. so certain artbitrary Government numbers need to be assigned, like value of carbon tax in environmental 'sustainability' calculations.

 

[renosteinke]

I am distressed by the discussion of circuit breakers in this thread.

First of all, because the links posted clearly -once you plow through them- do NOT apply to the sundry breakers we have in our household panels. For example, the 'trip test' method of applying 3x rated current is completely at odds with inverste time breaker operation and UL tests. NEMA, UL, and the breaker manufacturers themselved are united on this point: there's no way to 'test' a breaker's ability to trip at the desired level. There was even an ASTM standard withdrawn because of mis-application by 'used' equipment vendors.

More importantly, the discussion of breakers has pushed aside the discussion of the limited life of ALL equipment. To answer the OP, the NEC does not address this topic at all. The NEC is an installation standard, not an operations manual.

Everything, including enclosures, switches, receptacles, and wires, will 'age.' This aging is caused by simple time, and can be influenced by the specific environment. Conditions of use and maintenance will also have an effect. Now, the NEC does require that materials and methods be 'suitable' for the environment, and I can see an inspector asserting that something is inappropriate when there is evidence of damage- regardless of a code provision elsewhere that would seem to allow the use.

It's too easy, but 'let the market decide' certainly has a role here. There's a reason $20 receptacles are made and sold, despite the presence of $1 receptacles on the market. There are reasons folk buy QO instead of Homeline, and certain other brands are out of business.

Nor can any code change the simple fact that some folks are harder on things than others. In commercial TI work, I often see adjoining units where one is in nearly pristine shape, while its' immediate neighbor has broken receptacles, scorch marks at the switches, and flickering lights.

For the cynic, let me point out that the desire to 'choose the best' has led to several discussions here where objections have been raised to the use of 'commercial' appliances in homes. That enough folks would want to replace the $300 Mart-master appliance with a $10,000 Super-Pro to make this an issue... that is proof enough (to me) that folks really do want more than the 'least possible.'

 

[petersonra]

Do most MCBs have trip buttons? The only ones I recall seeing that way were larger frame sizes, and I think they were all electronic breakers.

Most places would get seriously offended if those breakers were turned off on any regular basis.

OTOH, I am not sure I ever looked that closely.

I went out in our shop and looked. Only found 2 MCBs. Both had trip buttons. Both of them tripped when I pushed the button. given as there was no power hooked up, I would have to bet this is not an electrical test of any kind.

 

[jim dungar]

I went out in our shop and looked. Only found 2 MCBs. Both had trip buttons. Both of them tripped when I pushed the button. given as there was no power hooked up, I would have to bet this is not an electrical test of any kind.

Just about every 480V molded case breaker greater than 150A has a Push-to-Trip button. This button actually operates the tripping, and therefore the reset, mechanism.

 

[T.M.Haja Sahib]

In some Government installations, the 'rated life' of 1.5 TR split Air-conditioner is six years.At the end of six years after installation,the A.C unit is scrapped irrespective of whether it is provided with a stand-by A.C unit or not.My objection is as below.Suppose the A.C unit and its stand-by are operated alternatively one on each day.At the end of six years period,each A.C unit would have completed only three years out of its 'rated life' of six years.So only at the end of twelve years from the date of installation of the A.C units,they should be scrapped.I think this kind of reasoning applies for all other equipments electrical or not.

It is not an economical life alone, it is obsolescence, which means both technological unsustainability and the uncontrolled cost escalation of repair. At the end it is always abot cost and indeed you were requesting cost data. What you're asking can not be calculated because the actual service is hardly determinable with any accuracy. so certain artbitrary Government numbers need to be assigned, like value of carbon tax in environmental 'sustainability' calculations.

 

[T.M.Haja Sahib]

Suppose you press the trip button of an installed molded case circuit breaker and it does not trip.Don't you think that the breaker has malfunctioned and it should be replaced ?

But the breaker must be electrically exercised regularly by pressing the trip button.If it does not trip,it should be replaced ( molded case circuit breakers).






As I've tried to explain it earlier, the manufacturer recommends the periodic, MECHANICAL excercise of the breakers.

 

[T.M.Haja Sahib]

Relatively new views against established convictions may have such effects.

I am distressed by the discussion of circuit breakers in this thread.]