Industrial Secondary Conductors Tap

[cdci]

I'm installing ACTIVE HARMONIC FILTERS to swbd's at an industrial site. The secondary of the xfmr is connected to swbd by 4000A bus to a 4000A main breaker. Then there are four 1200 breakers feeing MCC's.
The plant engineer wants me to tap off the 4000A bus, in the transition section upstream of the swbd main, to a 125A breaker, with less than 25' of #2 conductors. The City electrical inspector said that's ok. Citing sect, 240.21 C 3. His reasoning is Since the xfmr is not supplying any amps to the ACTIVE HARMONIC FILTER, the Filter is supplying up to 100A to the swbd, all the conductors should be sized to the filter.
This doesn't seem right to me. For my own peace of mind would like confirm this is ok. Don't want anyone getting hurt, and don't want an illegal installation.
Thanks for any info

 

[russ]

Re: Industrial Secondary Conductors Tap

I don't know anything about these harmonics filters your talking about, but could it fall under article 230.82.

Just chewing up paper, and spitting it in the air.

Russ

 

[cdci]

Re: Industrial Secondary Conductors Tap

FYI VFD's (variable frequency drives), welders, computers, fluorescent lighting, ect. distort the current waveform. Per IEEE 519 this harmonic distortion is not to exceed 5%. This unit will automatically sense the harmonics and inject current into the system to correct any harmonics on this swbd. In this case this unit can produce up to 100 AMPs of corrective harmonics and power factor. That's why the inspector says this unit is not using power, it is supply power.
hope this helps
This site has info on harmonics under Power Quality Articles and Books

[ March 27, 2003, 10:48 AM: Message edited by: cdci ]

 

[russ]

Re: Industrial Secondary Conductors Tap

If your harmonic fiter doesn't work under 230.82, I don't see it as a legal tap.

240.21(B)
(2) Taps Not Over 25 Ft (7.62 m) Long. Where the length of the tap conductors does not exceed 25 ft (7.62 m) and the tap conductors comply with all of the following.
(a) The ampacity of the tap conductors is not less than one third of the rating of the overcurrent device protecting the feeder

Russ

[ March 27, 2003, 07:18 PM: Message edited by: russ ]

 

[iwire]

Re: Industrial Secondary Conductors Tap

240.21(B) is a feeder tap wouldn't this be transformer secondary conductors which would mean 240.21(C)(3)

Which would mean the conductors would have to match the current rating of the transformer (4000 amps)

[ March 27, 2003, 07:31 PM: Message edited by: iwire ]

 

[ron]

Re: Industrial Secondary Conductors Tap

Can you give us the manufacturer and model # of the filter. It is difficult to imagine a device that recieves no power from its source, but can deliver 100A out. If the "xfmr is not supplying any amps to the ACTIVE HARMONIC FILTER", then why do you need a 125A breaker on the input side to the filter? I am being a wise a**, sorry. It definitly draws current on the input to the unit. Depending on the transformer size, you may be limited to your filter breaker, see Table 450.3(A) note 2.
IEEE 519 has limits for THD at the utility service (point of common coupling), not at a specific load. Someday, maybe we will have limits on individual loads like the european standards provide, but not yet, and not even close.

 

[iwire]

Re: Industrial Secondary Conductors Tap

I think it would be like a TVSS, the ones I have installed required #6 awg copper on a 50 amp breaker.

If you put an amprobe on it you will only see a few amps to run the lights and control board but I am sure when a surge hits the amps would go up as it tries to surpress the surge.

 

[cdci]

Re: Industrial Secondary Conductors Tap

Idon't believe this is a feeder tap, I'm tapping in front of main breaker. This falls under secondary conductors. I believe the conductors need to be rated for 4000A. Now, how do I (no nothing electrician) tell an electrical engineer and city inspector they're wrong and refuse to install that way?
But I think 240.21 C 2 would work because I see no reference to the xfmr rating. In 93 code this section made reference to no more than 1/10 of rating of xfmr. 02 code makes no such reference.
Bottom line... Would tapping #2 wire, less than 10', off a 4000A secondary bus, to a 125A breaker mounted on a wall be legal? 2002 code sect 240.21 C 2

Thanks for all your feed back

[ March 27, 2003, 08:41 PM: Message edited by: cdci ]

 

[iwire]

Re: Industrial Secondary Conductors Tap

IMO No, it would not be, now if you can get them to let you connect it on the load side of the 4000 amp MCB you could use 240.21(B) but as Russ said "(a) The ampacity of the tap conductors is not less than one third of the rating of the overcurrent device protecting the feeder"

This would still be over 1300 amps of conductor running to the line side of the 125 amp breaker, I have no idea how you would terminate that.

Any chance of going on the load side of the 4000 MCB and keeping the length under 10' then you could use all #2 awg

[ March 27, 2003, 08:21 PM: Message edited by: iwire ]

 

[cdci]

Re: Industrial Secondary Conductors Tap

Looks like replys were coming in as I was replying.
The unit is an ACCUSINE
LOW VOLTAGE ACCUSINE POWER CORRECTION SYSTEM
( AKA ACTIVE HARMONIC FILTER )

The company was bought out by SQ D

The power correction system shall be designed to electronically inject harmonic current to cancel the load produced harmonic current such that the upstream power harmonic current and voltage are reduced to below 5% TDD and 5% THD(V).
The units come in three sizes. 50, 100, and 300 Amp

site if you want tech. info
http://www.squared.com/us/misc/pspecs.nsf/unid/FFA2758A3A42FE0B85256A87006B5954/$file/specsFrameset.htm

You could think of this as a TVSS. But this cleans up distorted sine waves with current where TVSS aborbs votage spikes. You will see up to 100 Amps of current injected into power system from the Accusine.


Ron
That comment about not using any power came from the City inspector telling me it was legal to tap the sceondary with #2 wire.(And the plant engineer)I think they're both nuts telling me that it ok

 

[iwire]

Re: Industrial Secondary Conductors Tap

I understand they have different functions I was trying to get across that it will not have much current draw when it's not trying to control distorted sine waves.

 

[cdci]

Re: Industrial Secondary Conductors Tap

You don't have to read this. It's just my thinking through this and how to tell inspector he is wrong. Just ramblings of confused person.


Sect 240.21 B is a feeder tap. which means I'm tapping after a breaker. (in this case a 4000A MCB)
240.21 B (1) (4)
if I tap after a breaker in less than 10', the conductors must be 10% or greater than the feeder conductor. 4000A bus x 10% = 400 Amps
240.21 B (2) (1)
if I tap after a breaker in less than 25', the conductors must be aleast 1/3 the rating of the breaker. 1/3 of 4000A =1333 or 4-350MCM
So I don't want feeder tap.

Sect 240.21 C (3) 2002 code
(this is the one the electrical inspector said I could tap #2 wire, 25' to a 125 A breaker.)
if I tap off secondary of xfrm the conductors are not LESS than the secondary CURRENT RATING of xfmr--4000A--240.21 C (3) (1)
AND 240.21 C (3) (2) ALL overcurrent devices are GROUPED!! How can an inspector and engineer tell me its ok to tap with #2 wire?????????? plus 125A breaker is alone on wall.????


Sect 240.21 C (2) Not over 3' Maybe this will work
Sect 240.21 C (2) (1) the ampacity of secondary conductors is not less than combined loads on secondary conductors and not less than overcurrent device. --125 Amp breaker--
Sect 240.21 C (2) (2) the secondary conductors do not extend beyond the device they supply. --125 Amp breaker--
Sect 240.21 C (2) (3)the secondary conductors are in a raceway. #2's in a 1" conduit.
I can meet all the requirements in this sect. BUT!! I don't think that was the intent of this section that I can tap from the secondary. That's having parallel feeds from a tranformer, one at 4000A and one at 125A. IS THAT LEGAL????
What does in "one location mean"??? Is four 1200 A breakers in a swbd and one 125 A breaker mounted on a wall in front off the other four considered "one location"????

[ March 27, 2003, 10:12 PM: Message edited by: cdci ]

 

[ron]

Re: Industrial Secondary Conductors Tap

The ACCUSINE is a fancy signal generator. It generates harmonics of equal and opposite polarity from the harmonic on the feeder, to cancel it out.
See Table 450.3(A) note 2 for multiple feeders from a xfmr.

 

[iwire]

Re: Industrial Secondary Conductors Tap

They are not feeders unless on the load side of the 4000 Amp MCB, the original way was to tap the line side bus of the 400 amp MCB, this would make them transformer secondary conductors.

There is a large difference in fault current available depending on which side of the 4000 amp MCB you tap.

 

[cdci]

Re: Industrial Secondary Conductors Tap

iwre and Ron
Thanks for all the input.
All this comes down to is the inspector and engineer right or wrong in telling to me tap off a 4000A xfmr secondary, with #2 wire less than 25' to a 125 A breaker located on a wall, in front of four other breakers in a swbd.

After all this I still believe they're wrong and theres no way it can be done, unless "one location refers to a room and I can terminate 400A wire to a 125 A breaker.
And I forgot about the fault current.
Thanks

 

[ron]

Re: Industrial Secondary Conductors Tap

Fault current availability is the same on the line or load side of the 4000A circuit breaker, unless there are bad breaker contacts within causing resistance.