HVAC disconnect question

[grsthegreat]

Currently using a HACR breaker for my VRF unit.
Many just use a 60 A disconnect at the condensing unit
Haven't seen anyone use slow blow fuses at the unit in a long time

Thats pretty much the only way any contractor up my way does it. Most of the ac guys i worked with supplied me with a disconnect and fuses, they had disconnects with 2 small trouble lights inside unit. Easy for customer to know theres a bad fuse. Most all hvac supply houses up here supply those.

but now that im retired…..dont care much anymore.

 

[LittleBill21]

alright guys, why are fuses better then cb's? my hvac has been on a cb since the 90's, this is the first i heard of this.

 

[MAX-24-Dean]

alright guys, why are fuses better then cb's? my hvac has been on a cb since the 90's, this is the first i heard of this.

Subjective personal choice. Fuses or breakers, I will choose fuses everytime.
Fuses trip faster if sized correctly and will protect equipment and conductors at a higher fault current rating than a typical residential breaker.

 

[LouNY]

What I used on my mini-splits a few years ago were these non-fused disconnects, they look like breakers but are not, they are a simple switch.

Under $20 each and rain tite.

 

[grsthegreat]

What I used on my mini-splits a few years ago were these non-fused disconnects, they look like breakers but are not, they are a simple switch.
View attachment 779641

Under $20 each and rain tite.

There cheap, cause there useless. They offer no protection to the motor. Theres a reason all industrial motors choose to protect their expensive motors and electronics with fuses instead of relying on breakers.

 

[2manyrocks]

My Dad was an electrical engineer. He also preferred fuses because he said circuit breakers were mechanical devices that could stick in place if not routinely cycled to make sure they actually trip when needed.

 

[Boss 302]

The real purpose of the outdoor disconnect/pullout is to protect the person working on the equipment, as long as the breaker size matches what is called for on the equipment nameplate and it's HVAC rated (HVACR) then it does not need to be a fused disconnect/pullout and it meets the intension of the code.

 

[2manyrocks]

The location of the disconnect switch near the unit is also an opportunity to install surge protection near the unit. $30 for a fused disconnect and $70 for surge protection is a lot less than one service call to try to figure out what just fried the unit, much less trying to find the right parts and getting the unit running again.

Our electric power company intentionally rolled power outgages to keep the grid from failing over Christmas. Maybe it saved the grid, but the frequent on/off of the power supply from the utility company made me concerned that they were going to fry my HVAC systems in the process. As more demand is placed on the grid, I suspect this will only get worse as time goes on.

 

[LouNY]

There cheap, cause there useless. They offer no protection to the motor. Theres a reason all industrial motors choose to protect their expensive motors and electronics with fuses instead of relying on breakers.

No they are not motor protect devises and are not meet to be, the individual breakers that feed the switches are.
Also I have seen many breaker protect 3 phase 480 volt motors but there main protection is the motor overloads in the starters which may but not always also be fusible.

Also many are going solid state;

Electronic thermal overload relays measure current electronically, rather than relying on a heater mechanism, and so are insensitive to changes in ambient temperature. They’re also less prone to “nuisance,” or false, tripping. Electronic overload relays can provide data such as the percentage of thermal capacity utilization (%TCU), percentage of full-load amps (%FLA), time-to trip, current RMS, and ground fault current — information that can help operators conduct diagnostics and predict when the relay is at risk of tripping.

Electronic designs can also protect motors against phase loss (also referred to as phase failure), which occurs when one phase of current equals zero amps, often due to a short circuit or blown fuse. This causes the motor to draw excessive current on the remaining two phases and leads to significant motor heating.

 

[workinonit]

I've never heard this circuit breaker vs fuse theory. I don't doubt your knowledge and experience in the world of all things generator and electrical related but what I can tell you from years and years of my work in power plants all over the world is that most motors are protected by circuit breakers. You sometimes find fuses on some 480 volt motors but it's usually because feeding the motor from a circuit breaker isn't practical. And power plants have hundreds of motors. From servo drives to 20,000 HP ID and FD fan and large pump motors. If it's good enough for those I trust it on my condensing unit. I've installed hundreds of HVAC systems and pretty much all of them have the unfused disconnects if there was a properly sized breaker available. Those disconnects have zero to do with protecting the equipment. They are there to isolate the equipment for service. If you want to put a fused disconnect or circuit breaker on it, knock yourself out but it's not required.