480 volt Fused Switchgear

[Mbrooke]

Is there a manufacturer (Eaton, Siemens GE) that still offers 5000 amp fused switchgear standard? I can't find anything on their sites above 1,200 amp.

Second, is fused gear common in new installations? I see tons of buildings from the 70s with fused gear almost exclusively but everything new seems to be power circuit breakers.

 

[mparenteau]

I don't rep an OEM, but I haven't seen anything remotely fitting that description for a long time. Any particular reason why you can't use circuit breakers?
Mike

 

[Mbrooke]

Selective coordination, 200ka interrupting current and lower cost.

Fused discos used to be the norm but I'm not sure what happened.

 

[mparenteau]

"Fused discos used to be the norm but I'm not sure what happened. " - at 5000 amps? I wonder about that statement.

Anyway, what is your maximum, 3 phase fault current available at your proposed equipment location? Also, are you able to segregate your service into two (or more) smaller ones? Arc flash concerns...

Mike

 

[che12345]

Dear Mr Mbrooke

1. Is there any 5000A fuse you come across? No, impossible.
2. Almost all ACB manufacturers do have their breakers current rated up to 6300A and some even higher. And do have short circuit making capacity up to 330kA.
3. If Iu=6.3kA and Icm=330kA is [not sufficient for your application], then it is likely you had chosen an over-sized MVA or a too low Z% transformer.
4. Are you able to segregate your service into two (or more) smaller ones? Arc flash concerns...as pointed out by learned Mr mparenteau.
5. As you had observed, breaker is "current" while fuse is "obsoleted". There are many reasons for this taking over and there will never be any U-turn. A breaker can have far more functionalities, adjustments, remote switching/monitoring etc. A breaker by design prevents [single-phasing] which happens " rather often?" with fuse, which has no remote monitoring possibility.

Che Kuan Yau (Singapore)

 

[dpc]

I'd check wtih Eaton/Cutler Hammer. They still make Pringle bolted pressure switches up to 5000 A, I think. Maybe 6000 A. I'm not a fan of these, but they have been around a long time.

Dave

 

[Mbrooke]

1. Is there any 5000A fuse you come across? No, impossible.

Why impossible? Ive seen plenty of KRPs and other older vintage styles:

http://www.cooperindustries.com/con.../fuses-lv-ul-csa-branch/class-l/krp-c-sp.html

2. Almost all ACB manufacturers do have their breakers current rated up to 6300A and some even higher. And do have short circuit making capacity up to 330kA.

Can you link me 330ka ACBs?

3. If Iu=6.3kA and Icm=330kA is [not sufficient for your application], then it is likely you had chosen an over-sized MVA or a too low Z% transformer.

Or you have no option. Con Edison lists most services as to be considered having an available short circuit ampacity of 200,000 amps.

4. Are you able to segregate your service into two (or more) smaller ones? Arc flash concerns...as pointed out by learned Mr mparenteau.

Not always, sometimes the AHJ will not allow it. NEC wants one service per building typically.

5. As you had observed, breaker is "current" while fuse is "obsoleted".

Why obsolete? Fuses are in many ways still superior.

There are many reasons for this taking over and there will never be any U-turn.

There is already a U turn in life safety circuits:

http://www.cooperindustries.com/con...ards/quik-spectm_coordinationpanelboard1.html

Sometimes molded case breakers/MCCBs/ACBs will just not coordinate.

A breaker can have far more functionalities, adjustments, remote switching/monitoring etc.

Who says I need all that? Am I protecting transmission lines or LV feeders? Do you seriously believe a building owner wants to shell out more money on something he neither understands nor has practical need for?

A breaker by design prevents [single-phasing] which happens " rather often?" with fuse, which has no remote monitoring possibility.

Che Kuan Yau (Singapore)

If the loads and MCC already have it, there is less need. Also the owner may not want to re-set breakers after a single phase event at the POCO.

 

[Mbrooke]

@dpc: Do they still make the complete gear standard?

@mparenteau: yes, even at 5,000amps. Often the main switch board had a fused main and 12 (give or take) fused branches.

 

[aussiejohn2]

All,
In principle fuses can have some of the capability often ascribed only to CBs.
* You can have remote indication, either by striker pins or by monitoring the voltage across them.
* Striker pins allow for ganged operation.
There are even medium voltage multi-shot reclosers using fuses (although their mechanical reliability is questioned).
However they are increasingly difficult to obtain these features commercially, at all voltages. I think people are hypnotised by the blinkenlights and apparent "modernity" of CBs (and vendors make more from CBs). As well as the advantages MBrooke has listed for fuses, the fast clearing time can help with arc flash.
John.

 

[Mbrooke]

and vendors make more from CBs

^^^This. Fuses are just to cheap all the way around. The electrical manufacturers already own the NFPA and are presently trying to take over the IEC. So marketing CBs while demonizing fuses is a leisure endeavor by comparison.


One big plus: a breaker that have never opened in 30 years may jam, where as a fuse will not fail in the same scenario.

 

[mparenteau]

@MBrooke:

Can you point to the NEC reference that says, "NEC wants one service per building typically."

Mike

 

[Mbrooke]

From the 2017 NEC

230.2 Number of Services. A building or other structure
served shall be supplied by only one service unless permitted in
230.2(A) through (D). For the purpose of 230.40, Exception
No. 2 only, underground sets of conductors, 1/0 AWG and
larger, running to the same location and connected together at
their supply end but not connected together at their load end
shall be considered to be supplying one service.


(A) Special Conditions. Additional services shall be permitted
to supply the following:
(1) Fire pumps
(2) Emergency systems
(3) Legally required standby systems
(4) Optional standby systems
(5) Parallel power production systems
(6) Systems designed for connection to multiple sources of
supply for the purpose of enhanced reliability


(B) Special Occupancies. By special permission, additional
services shall be permitted for either of the following:
(1) Multiple-occupancy buildings where there is no available
space for service equipment accessible to all occupants
(2) A single building or other structure sufficiently large to
make two or more services necessary


(C) Capacity Requirements. Additional services shall be
permitted under any of the following:
(1) Where the capacity requirements are in excess of
2000 amperes at a supply voltage of 1000 volts or less
(2) Where the load requirements of a single-phase installation
are greater than the serving agency normally
supplies through one service
(3) By special permission


(D) Different Characteristics. Additional services shall be
permitted for different voltages, frequencies, or phases, or for
different uses, such as for different rate schedules.


(E) Identification. Where a building or structure is supplied
by more than one service, or any combination of branch
circuits, feeders, and services, a permanent plaque or directory
shall be installed at each service disconnect location denoting
all other services, feeders, and branch circuits supplying that
building or structure and the area served by each. See 225.37.

230.40 Number of Service-Entrance Conductor Sets. Each
service drop, set of overhead service conductors, set of underground
service conductors, or service lateral shall supply only
one set of service-entrance conductors.

Exception No. 2: Where two to six service disconnecting means in separate
enclosures are grouped at one location and supply separate loads
from one service drop, set of overhead service conductors, set of underground
service conductors, or service lateral, one set of service-entrance
conductors shall be permitted to supply each or several such service
equipment enclosures.

If you really wanted to you can have multiple services to a building, but at the same time if the power company of AHJ really wants one service they have strong ground to argue their case. You'd think over 2000amps would save you, but the powers that be still want a single service.

 

[rcw retired EE]

Some high density areas, with high rise buildings and a legacy LV network have 200kA or higher short circuits. Network transformers supply power to the "grid" network at multiple locations. A service taps the LV grid directly without a dedicated transformer. Using two services to the building doesn't help. Both services are at 200kA short circuit. Downtown Seattle and San Francisco used to be like that with very high arc flash. Fuses were the only choice. (I don't know what the present systems are).

 

[mparenteau]

@Mbrooke:

Ahh..forgot about that code reference. Thanks for keeping me honest. I've seen a number of multiple service entrance installations...no issues with those apparently (more about the reliability section referenced above).

Mike

 

[dpc]

Mbrooke:

I'm not sure if they'll quote a complete switchboard of fused switches. I'd just check with Cutler Hammer. They have a semi-custom shop up here in the PNW where they used to build all manner of interesting things.

 

[Mbrooke]

Any info as to why? I'm noticing that manufacturers are a lot less enthusiastic.


@rcwilson: Don't forget Bronx, Brooklyn, Queens and Manhattan. Even if the building isn't served by a secondary network, it will universally be served via spot networks. 5 x 1,500kva 5% Z paralleled transformers make for limited options. On the plus side you can lose 2 13.8 or 27.6kv cables and still have power without overloading anything.

 

[wbd]

S&C Electric makes fused switchgear from 5kV to 34.5kV

 

[Mbrooke]

They are great, but nothing the 600 volt and under class.