MCCB + Contactor Feeder 1

[NickParker]

Why MCCB+Contactor is used for Non-Motor circuits?

I understand using MCCB + Contactor if it is an application of frequent start/stop, . Are there any other reasons to use MCCB+Contactor for a transformer/other feeder?

 

[xnuke]

I've used this configuration for remote control of load shed/add in islanded microgrids, which will be done by the contactor, not the MCCB. While a MCCB may be provided with a shunt trip for remote load shed, it can't do remote load add without a motor operator, which is an expensive bulky add-on for that type of breaker.

Note that switching a feeder to a transformer may require contactor derating due to the high inductive load.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[che12345]

Dear Mr. NickParker (Electrical)(OP)10 Jan 23 13:20
"....Why MCCB+Contactor is used for Non-Motor circuits? "
I am fully in agreement with learned advice by Mr. xnuke
I only wish to submit the following for general information purposes:
1. MCCBs are NOT mechanically designed for:
(a) high frequency of ( i.e. on-off-on ) switching within a short time continuously,
(b) high number of electrical and mechanical operations.
1.1. Contactors are design for high frequency and numbers of electrical and mechanical operations.
2. In this MCCB in series with Contactor arrangement, for higher reliability reasons; the combination should be Type 2 co-ordination . See IEC for detail. In brief, the MCCB shall trip for any short-circuit but the Contactor shall NOT be damaged but should be inspected which is allowed (to break open the lightly-welded contacts), if any.
3. Note: The terminology Type 2 coordination is used in IEC world. It is unknow/not used in the US, ANSI, UL, NEMA, NEC....
Che Kuan Yau (Singapore)

 

[Parchie]

An air circuit breaker can do the same function as that contactor.

 

[che12345]

@ Dear Mr. Parchie (Electrical)11 Jan 23 03:30
"....An air circuit breaker can do the same function as that contactor."
1. An air circuit breaker (ACB) we usually refer to breakers > 1kA to 630kA. MCCBs are generally say 10A to 630A. ACBs at a higher cost are always of heavier mechanically built, withstand higher SC kA in 1s or 3s. MCCB are NOT rated for 1s rating.
1.1. Contactors are also NOT 1s rated.
2. Both ACB and MCCB are NOT designed to function as a Contactor, which is designed for high frequency of on-off-on switching and durable for large numbers of mechanical and electrical operations.
3. The Contactor may NOT be replaced by an ACB unless it is of very infrequent switching. In that case the MCCB alone without the Contactor would be fine.
4. A motorized + with shunt release MCCB can perform remote switching.
Che Kuan Yau (Singapore)

 

[Parchie]

@che12345,
That's precisely why I replied that way. The OP was mentioning about the question of why the installation is using the MCCB + contactor when the use does not involve frequent ON/OFF! Are you assuming there are frequent starts/stops? My read is that the OP specifically mentioned the opposite.

 

[che12345]

@ Mr. Parchie (Electrical)12 Jan 23 07:05
"...@che12345,...That's precisely why I replied that way. The OP was mentioning about the question of why the installation is using the MCCB + contactor when the use does not involve frequent ON/OFF! Are you assuming there are frequent starts/stops? My read is that the OP specifically mentioned the opposite."
I do NOT make any assumption. I pointed out the general principle:
(a) ACBs and MCCBs are NOT designed for [high frequent of on-off-on switching] and [large number of electrical and mechanical operation]. (b) Therefore both ACB/MCCB are NOT a suitable replacement of the Contactor.
2. For infrequent switching, the MCCB alone (without) Contactor would be fine. In case of frequent switching, (MCCB+Contactor) is a good proposal.
3. In all cases an ACB (1-6.3kA) would be more expensive and with bigger physical size than a MCCB (10-630A), of the same current rating. Therefore, MCCB is preferred if the current rating and SC kA ratings are suitable at the location of the installation.
Che Kuan Yau (Singapore)

 

[Maximillianrichards]

Hi!

Parchie, che12345

From [URL unfurl="true"]https://www.asutpp.com/circuit-breaker.html[/url]

An air circuit-breaker is a circuit-breaker in which the contacts open and close in the air at atmospheric pressure.

MCCB (Molded Case Circuit Breaker) and contactor combinations are commonly used for non-motor circuits because they provide several benefits, including:

[ol 1]
[li]Overload and short-circuit protection: MCCBs can provide reliable protection against overloads and short-circuits in non-motor circuits. The contactor is used to control the switching of the circuit, while the MCCB protects the circuit against overloads and short-circuits.[/li]
[li]Remote operation: The contactor provides remote operation of the circuit, allowing the circuit to be controlled by a switch or relay located in a different part of the system.[/li]
[li]Switching of high-current loads: MCCBs can handle high-current loads, making them suitable for use in circuits with large loads, such as lighting or heating systems.[/li]
[li]Space-saving: MCCB and contactor combinations can help to save space in a control panel or switchgear, as they provide both switching and protection functions in a single unit.[/li]
[/ol]

 

[thermionic1]

I've seen this used for small transformer switching, as part of a LV MCC. I believe an unmentioned benefit is that the "bucket" is somewhat interchangeable so 1 spare for a given class/size can be used for motor or transformer application with minor adjustments to O/L.