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HVAC Equipment and Phase Loss

HVAC Equipment and Phase Loss

HVAC Equipment and Phase Loss

(OP)
In a few days, I will be performing an inspection at a property that reportedly suffered from phase loss, followed by damage to three-phase HVAC equipment. At this time, I'm not sure if damages involve air handling units, condensing units, packaged rooftop units, chillers, pumps, or a combination of these.

A few questions:

1. Why are phase loss protection relays not included as standard features on three-phase HVAC equipment?
2. I generally understand (or like to think that I understand) the mechanism by which phase loss results in damage to a three-phase motor that is in operation, but why don't motor overloads provide adequate protection in this case? Is it simply a matter of insufficient reaction time?

RE: HVAC Equipment and Phase Loss

1. It adds $150 to the cost and the HVAC industry is notoriously cheap.

2. Some types of OL relays will eventually trip on a phase loss, but refer to issue #1. They go with the cheapest thing they can legally get away with.

There is of course nothing stopping an end user from protecting their investment by having phase loss protection in the installation, but there too, the work tends to go to the lowest bidder so if it isn’t in the procurement requirements, the bottom feeders will not add it in.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: HVAC Equipment and Phase Loss

Everything Jeff stated.

Seen tons of it!
Had many conversations;
"You should consider phase loss detection to protect your system."

"Don't want to spend the money."

"Two hundred bucks installed to protect a $10k piece of critical machinery keeping perishables safe?. Seriously?"

"We have pretty reliable power here."

"For the record you're nutz."

=====
You'll be likely to find a compressor burnout with a completely acid washed down-stream system that will require a complete and complex clean-out remediation effort.

Keith Cress
kcress - http://www.flaminsystems.com

RE: HVAC Equipment and Phase Loss

Every phase loss is my business gain. Ka-ching you chumps.

Seriously though, once I tell my clients that my repair warranty won't cover single phasing, most of them do install that protection.

Muthu
www.edison.co.in

RE: HVAC Equipment and Phase Loss

Dear Mr. jmbelectrical (Electrical)(OP)26 Jun 22 18:02
" ... I'm not sure #0. if damages involve air handling units, condensing units, packaged rooftop units, chillers, pumps, or a combination of these.
A few questions:
#1. Why are phase loss protection relays not included as standard features on three-phase HVAC equipment?
#2. I generally understand .... the mechanism by which phase loss results in damage to a three-phase motor that is in operation,
#3. but why don't motor overloads provide adequate protection in this case? Is it simply a matter of insufficient reaction time?..."

#0. (Single-phasing damage) involve ALL [three-phase equipments], be it AHU, condensing unit etc.
#1. Cost is the major consideration. The other problem is by installing ONE unit monitoring the incoming is NOT good enough. Single-phasing can happen in any three-phase equipments. It would be a major cost factor to install single-phasing protection on ALL three-phase equipments.
#2. Yes . See above #0.
#3. In Europe, most recent especially electronic thermal overloads include with single-phasing protection. But there are many old thermal over-load units in the field without this feature.
#4. FYI: Attention! Any three-phase circuits/equipments that is protected by fuses, single-phasing may happen " any time any place". It is strongly recommended to replace all three-phase fuses with three-phase breaker. Single-phasing with breaker is extremely low.
Che Kuan Yau (Singapore)-

RE: HVAC Equipment and Phase Loss

Careful on the issue of replacing fuses with circuit breakers. If there are any power electronics in the equipment, such as Variable Frequency Drives (VFDs), Electronically Commutated Motors (ECMs) or Reduced Voltage Solid State (RVSS) starters, which are all very common in HVAC equipment now, rules for the listing/approved use of those devices has been shifting to requiring fuses; breakers alone are no longer going to be acceptable. Most power electronics will have built-in phase loss protection anyway so that issue wouldn’t apply, this is just a general warning against the blanket replacement of fuses with circuit breakers.

Tied into this is the issue of the Short Circuit Current Rating (SCCR) of the equipment. If the equipment vendor used fuses to attain an SCCR necessary for it to be installed at your site and you replace those fuses with breakers, you may have violated the SCCR listing and made your installation non-compliant. Details matter, so it’s not appropriate in some cases.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: HVAC Equipment and Phase Loss

Dear Mr. jmbelectrical (Electrical)(OP)26 Jun 22 18:02
I would like to post the following personal opinion, for your consideration.
1. Yes. [ a fast-speed fuse offers better protection than a current-limiting circuit breaker] for semiconductor devices (e.g. VFD etc...)
2. The down side with fast-speed fuse are
a) not readily available on the market place. Even the manufacturer takes couple of weeks to deliver the product,
b) not replaceable by any other normal fuses used in the field or available on the market place,
c) high price,
d) does not prevent single-phasing that you are facing,
e) it does not prevent semiconductor device from failure but helpful in containing the fault/arc/fire/damage,
f) When the fuse blows, the whole VFD is close to gone.
Che Kuan Yau (Singapore)

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