Branch Circuit or Single Feed

[padawan learner]

Purchased 1400kVAr Power Factor and Harmonic Filter unit made of 2 enclosures. The rated capacitor current is 1682A total. Sized the ocpd to feed the unit at 135% X 1682=2270A which is a 2500A breaker and installed it into the switchgear (all with the blessing, "yes this is right", from the application engineer). When the "unit" arrived, it has bus bars in each of the two enclosures with 700kVAr split into each panel. There is one controller that turns on stages of caps/reactors in both panels.

The 2500A ocpd is still the right size for a feeder. Do I have to consider the feed to each enclosure as a branch and follow the rules of feeder taps in 240.21? Or since it is controlled as a unit, can I consider it to be one unit and still split the feed into half for each enclosure and not worry about the feeder tap rules? The run of wire from the 2500 ocpd to the panels is well less than 25'.

Thanks for any help.

 

[Smart $]

I have considered your description and keep coming back to two issues...

First is that you say one controller for both enclosures, but you also make it sound as though each enclosure is supplied separately. Need more detail, as that sounds quite odd.

Second is...

ARTICLE 460
Capacitors
460.8 Conductors.
....
(B) Overcurrent Protection. An overcurrent device shall be provided in each ungrounded conductor for each capacitor bank. The rating or setting of the overcurrent device shall be as low as practicable.

Exception: A separate overcurrent device shall not be required for a capacitor connected on the load side of a motor overload protective device.

How does the manufacturer's instructions say the enclosures are to be supplied and interconnected?

 

[padawan learner]

The controller turns on/off "stages" of 50 kVAr based on the need for power factor correction of the system. There are 14 stages in one enclosure and 14 stages in the other. If the power factor of the system is very bad, then the controller would close contactors feeding a stage until enough stages were powered to reach the desired power factor. Within the panel, each capacitor bank/stage is fused, individually which should meet the 460.8 requirement.

The Mfg. instructions are below.

Circuit Breaker​

The circuit breaker should be sized no less than 135% of the ratedcapacitor current. (which is why when I sized my CB at 2500A for 1400kVAr, mfg. did not indicate that the feed would be split to the two panels)​

Note: ​

Rated Capacitor Current = (1000 x kVAr) / (3 x Voltage)(Amps)Where: Voltage = line to line voltagekVAr = 3 phase kVAr rating of capacitor (Nameplate rating)Example: 500 kVAr capacitor, 480 V system:Rated Capacitor Current =​

(1000 x 500) / (3 x 480) = 601 Amps

 

[Smart $]

The controller turns on/off "stages" of 50 kVAr based on the need for power factor correction of the system. There are 14 stages in one enclosure and 14 stages in the other. If the power factor of the system is very bad, then the controller would close contactors feeding a stage until enough stages were powered to reach the desired power factor. Within the panel, each capacitor bank/stage is fused, individually which should meet the 460.8 requirement.

The Mfg. instructions are below.

Circuit Breaker​

The circuit breaker should be sized no less than 135% of the ratedcapacitor current. (which is why when I sized my CB at 2500A for 1400kVAr, mfg. did not indicate that the feed would be split to the two panels)​

Note: ​

Rated Capacitor Current = (1000 x kVAr) / (3 x Voltage)(Amps)Where: Voltage = line to line voltagekVAr = 3 phase kVAr rating of capacitor (Nameplate rating)Example: 500 kVAr capacitor, 480 V system:Rated Capacitor Current =​

(1000 x 500) / (3 x 480) = 601 Amps

Well, we're getting closer. We now know the controller controls contactors, and each bank/stage is fused. Is the fusing between contactor and capacitors, or is the contactors between the fusing and the cap's. More importantly, what do your incoming lines connect to? How many incoming line terminals, and in which enclosure?

You say there is one controller. Are you counting the contactors as part of the controller? Where are the contactors located? Essentially, what is in [E1]? What is in [E2]? ...and how are the internals connected?

Short of providing pictures, diagrams, schematics of and/or links to the pertinent information, any conclusion would just be speculation. Please be as explicit as possible if you have to resort to textual descriptions. This is not the psychic hotline. We do not read minds. The answer to what seems like a simple question is hidden in the details.

 

[padawan learner]

As much as I would like for this to be able to be called one unit, after sleeping on it, I cannot see any way around having to follow feeder tap rules for the conductors to each enclosure. At the load side of the 2500A breaker the feed is split into two equal 700kVAr loads.

Thanks for your help.

 

[topgone]

As much as I would like for this to be able to be called one unit, after sleeping on it, I cannot see any way around having to follow feeder tap rules for the conductors to each enclosure. At the load side of the 2500A breaker the feed is split into two equal 700kVAr loads.

Thanks for your help.

You don't have to worry much since most OEM's almost always provide fuses in each step, per my own experience. Besides, it is a switching PFC (stepped at 50 kVA per step), IMO. Just see if your units are provided with fuses, to be sure and your good.

 

[Smart $]

As much as I would like for this to be able to be called one unit, after sleeping on it, I cannot see any way around having to follow feeder tap rules for the conductors to each enclosure. At the load side of the 2500A breaker the feed is split into two equal 700kVAr loads.

Thanks for your help.

You don't have to worry much since most OEM's almost always provide fuses in each step, per my own experience. Besides, it is a switching PFC (stepped at 50 kVA per step), IMO. Just see if your units are provided with fuses, to be sure and your good.

My latest questions eluded to the following requirement for taps >10', <=25' (based on OP)...

The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.