Electronics tech needs help with wire sizing for AC and elevator

RobertKLR

Member
Location
Texas
I am an electronics tech but I fill an electrician's position at a VA hospital. It's a long story why this VA does not use real electricians but that's another thread. Recently an HVAC system has started tripping a 70 amp breaker (3ph, 460V) (elevator also on the circuit). The breaker is located in one building and feeds another building 330 ft away. I've corrected some of the issues and reduced the nuisance tripping to an "acceptable" level (not acceptable to me but the bosses have quit complaining). One of the issues was the panel room was so hot in the area of the breaker (rated 104F but the breaker temp was 110F). That was corrected by adjusting the room's ventilation, the breaker is now at about 95F but I've since learned that other devices were added to the circuit before I came to work here that were never recorded, I just stumbled across them. So now I'm thinking that the 70 amp breaker is no longer adequate and the breaker and wiring should be for 150 amps. I'm basing that on measuring continuous power at 47 amps and non continuous at 91 amps ((47x1.25)+91)). Is this correct?

Like I said I'm an electronics tech, not an electrician, but I'm all they have right now. There is no funding available to have a contractor come in and deal with this right now, that may be a year away and the affected building is the OI&T building with the medical servers in it. Now I understand the physics of the issue but I'm not so strong on the code and the required calculations. So, the existing wire size is 2 awg with THW insulation (330ft). The current breaker is a 70 amp CH FS340070A. Can I go to a 90 or 100 amp breaker with what I described or am I heading down the wrong road?
 

RobertKLR

Member
Location
Texas
the elevator AND the hvac unit are on the same 70 A ckt?
does the hvac serve the elevator room?
The elevator and hvac are on the same breaker but the hvac serves the entire 3 story 70+ yr old building. This is also the OI&T building and when the hvac system stops that old building heats up fast.

I'll add the building power is 120 and 208. That's why the 460 had to be brought in from the nearby building. This is the VA, there is no rhyme or reason to why they do things the way they do.
 

growler

Senior Member
Location
Atlanta,GA
This is the VA, there is no rhyme or reason to why they do things the way they do.
If it's Federally owned property it's not subject to local inspections for one things.

I'm surprised they could get the elevator certified with it hooked up like this but maybe they didn't have to.


Edit: Find out who the authority having jurisdiction over this property is. Then question them as to any changes you wish to make. Then get any response in writing.

Allways put the monkey on the other guys back because you are not qualified to make these decisions.
 
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GoldDigger

Moderator
Staff member
turn off the hvac when elevator runs.
definitely sounds like a re-wire, but not using 150A ocpd.
Probably not practical depending on how often the elevator runs and the limitation on starts for the compressors and fan motors.
It may be useful, if possible, to prevent A/C *starting* while the elevator is climbing.

Sent from my XT1585 using Tapatalk
 
Last edited:

RobertKLR

Member
Location
Texas
If it's Federally owned property it's not subject to local inspections for one things.

I'm surprised they could get the elevator certified with it hooked up like this but maybe they didn't have to.


Edit: Find out who the authority having jurisdiction over this property is. Then question them as to any changes you wish to make. Then get any response in writing.

Allways put the monkey on the other guys back because you are not qualified to make these decisions.
I've already done that but getting VA management to weigh in on anything is problematic. I'm always having to go outside the VA to get answers because within the VA there is no functional avenue for technical advice. Right now I've been able to get it operating well enough but I would rather get it right. My normal duties are taking care of the non medical electronics but as I said we haven't had a real electrician here in over 7 years so I've been filling in. When we have money I can get contractors to help out but right now the money is not there.
 

FionaZuppa

Senior Member
Location
AZ
Probably not practical depending on how often the elevator runs and the limitation on starts for the compressors and fan motors.
It may be useful, if possible, to prevent A/C *starting* while the elevator is climbing.

Sent from my XT1585 using Tapatalk
me being sarcastic ;)

if the ckt is being overloaded, what other options are there then to provide a new ckt to one or the other.
personally, HVAC sounds more important, i would install new ckt for hvac and change ocpd for the vator/lift.
 

RobertKLR

Member
Location
Texas
Probably not practical depending on how often the elevator runs and the limitation on starts for the compressors and fan motors.
It may be useful, if possible, to prevent A/C *starting* while the elevator is climbing.

Sent from my XT1585 using Tapatalk
I have entertained that thought (I have a plc and parts that could control such a thing) but I'm just wondering if it would be practical to put a 90 or 100 amp breaker in with the existing wiring until the funds are released to get it all done correctly. That could be months away.
 

RobertKLR

Member
Location
Texas
me being sarcastic ;)

if the ckt is being overloaded, what other options are there then to provide a new ckt to one or the other.
personally, HVAC sounds more important, i would install new ckt for hvac and change ocpd for the vator/lift.
Definitely the hvac is the winner, this is west Texas and it is a very hot summer.
 

GoldDigger

Moderator
Staff member
If you are looking at temporary measures, blowing a fan on the breaker is a classic.
Theoretically you are also allowed to upsize the breaker if the ambient temperature is *consistently* high.

Sent from my XT1585 using Tapatalk
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I am an electronics tech but I fill an electrician's position at a VA hospital. It's a long story why this VA does not use real electricians but that's another thread. Recently an HVAC system has started tripping a 70 amp breaker (3ph, 460V) (elevator also on the circuit). The breaker is located in one building and feeds another building 330 ft away. I've corrected some of the issues and reduced the nuisance tripping to an "acceptable" level (not acceptable to me but the bosses have quit complaining). One of the issues was the panel room was so hot in the area of the breaker (rated 104F but the breaker temp was 110F). That was corrected by adjusting the room's ventilation, the breaker is now at about 95F but I've since learned that other devices were added to the circuit before I came to work here that were never recorded, I just stumbled across them. So now I'm thinking that the 70 amp breaker is no longer adequate and the breaker and wiring should be for 150 amps. I'm basing that on measuring continuous power at 47 amps and non continuous at 91 amps ((47x1.25)+91)). Is this correct?

Like I said I'm an electronics tech, not an electrician, but I'm all they have right now. There is no funding available to have a contractor come in and deal with this right now, that may be a year away and the affected building is the OI&T building with the medical servers in it. Now I understand the physics of the issue but I'm not so strong on the code and the required calculations. So, the existing wire size is 2 awg with THW insulation (330ft). The current breaker is a 70 amp CH FS340070A. Can I go to a 90 or 100 amp breaker with what I described or am I heading down the wrong road?
There are a lot of issues associated with this that probably need to be explored to actually "fix" it.

I am not even sure it is allowed by code to have an HVAC system on an elevator circuit.

Normally you are only allowed a single feeder to a building. it seems likely given your description of the situation that you have more than one.

Load calculations are based on the requirements for such calculations found in article 220.

No offense, but I am kind of afraid to even offer suggestions given your level of competence. You might end up making it worse just from not knowing what questions to ask, and what is important.

Personally I like the idea of just shutting off the A/C compressor while the elevator is starting. It has simplicity going for it. But as another poster mentioned it might create problems with the A/C motor and allowed starts. If the elevator is used a lot you might end up with little or no A/C.

#2 copper is good for 115 A depending on what type of insulation it has. My suspicion is that it is AL which is only good for 90 A. that would kind of make sense given the load and the distance the conductor runs.
 

RobertKLR

Member
Location
Texas
There are a lot of issues associated with this that probably need to be explored to actually "fix" it.

I am not even sure it is allowed by code to have an HVAC system on an elevator circuit.

Normally you are only allowed a single feeder to a building. it seems likely given your description of the situation that you have more than one.

Load calculations are based on the requirements for such calculations found in article 220.

No offense, but I am kind of afraid to even offer suggestions given your level of competence. You might end up making it worse just from not knowing what questions to ask, and what is important.

Personally I like the idea of just shutting off the A/C compressor while the elevator is starting. It has simplicity going for it. But as another poster mentioned it might create problems with the A/C motor and allowed starts. If the elevator is used a lot you might end up with little or no A/C.

#2 copper is good for 115 A depending on what type of insulation it has. My suspicion is that it is AL which is only good for 90 A. that would kind of make sense given the load and the distance the conductor runs.
I agree with your assessment of my level of competence. I have extensive electronics training but the technicalities of the electrician field is not part of that training, so no offense taken. I've certainly appreciated the responses so far also. Someone mentioned putting a fan on the breaker and that is what I did until I was able to get the air flow moving like it should through the panel room. These are old buildings, remodeled many times and the ductwork is a mess.

There are two feeders to the building in question, one comes straight from the switchgear building (13.2KV) to a transformer for the 208 power but the hvac and elevator are fed from another building across the street which has 460vac.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
There are two feeders to the building in question, one comes straight from the switchgear building (13.2KV) to a transformer for the 208 power but the hvac and elevator are fed from another building across the street which has 460vac.
That kind of makes sense.

I wonder why they did not just set another xfmr in there instead of running 480 from another building? Not that it matters much at this point. Probably to save a buck or two.

About the only thing you can do is up size the breaker to the max allowed for the wire you have. But I am not thrilled with the idea of suggesting you do it given that you could potentially kill yourself trying it due to lack of knowledge on how to do so in a safe way. Not knowing how to do it right might also cause you to do it wrong in a catastrophic way that might not kill you but might create serious damage.
 

Ingenieur

Senior Member
Location
Earth
The elevator and hvac are on the same breaker but the hvac serves the entire 3 story 70+ yr old building. This is also the OI&T building and when the hvac system stops that old building heats up fast.

I'll add the building power is 120 and 208. That's why the 460 had to be brought in from the nearby building. This is the VA, there is no rhyme or reason to why they do things the way they do.
pretty sure this an NEC and A17 violation
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
pretty sure this an NEC and A17 violation
That would have been my guess. But I wonder if what he meant was that they are on the same feeder, and not the same branch circuit.

It's still a code violation if you don't have adequately sized feeders.

There is so very little we know about this installation from what he is telling us.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It's an NEC violation for the disconnecting means of an elevator circuit to be disconnected by any other means than the elevator system. In fact you cannot even run the HVAC for the elevator on the same branch circuit of an elevator, it must have it's own branch circuit. So if that breaker is the only OCPD in the elevator system, then it is the BRANCH OCPD for the elevator and that alone disallows the use of that same circuit to be used by both systems. If on the other hand the 70A breaker is a FEEDER, not a branch OCPD, then there must be branch OCPDs somewhere down stream of this 70A breaker for BOTH the elevator AND the HVAC. If so, but it is the FEEDER that is tripping, not the branch OCPDs, then something was incorrectly sized.
 

RobertKLR

Member
Location
Texas
I really appreciate the comments and there has been some good advice in them. I've summarized some of the comments in an email to the chief engineer and safety director. I then went to the union and requested they also push for a contractor to assess the situation.
 
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