1/4 by 1 1/4 fuses

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Weidmuller makes a fuse holder for cl1 div2 locations yet i am unable to find any fuses that are certified for this location. Bussman makes sealed fuses that are sealed for board washing cycles but they won't commit to saying they are hemetically sealed. They also make a very fast acting filled type "GBB", would these be considered current limiting? Has anyone purchased certified c1d2 1 by 1.25" fuses?


Senior Member
I recall some Bussmann 1/4 x 1-1/4 fuses that were powder filled that may work, but the powder filled versions were only 15A and 20A or something fairly large - the lower amperages in the same line were ordinary glass fuses that cannot be used in C1D2.

We typically use Midget/Class CC fuses, Bussmann KTK, Shawmut ATM, or similar. The fuseholders take up about 1/2" on DIN rail - I assume you're looking for something smaller where the holder will take up less space in the box?

I'm not sure what Weidmuller fuseholder you're referring to, but there's nothing special about a fuse holder that makes it suitable for C1D2 - you have a lot more flexibility here than you may realize - manufacturers like to take ordinary products, slap a Div 2 label on them and sell them for more $$ because a lot of people don't know the C1D2 code rules. This is a bit like UL - the vast majority of electrical products are not required to be UL listed, yet some people want UL on all sort of things where it isn't required and doesn't lead to a better design or better installation.


Senior Member
It looks like you're getting lulled into the "certified for hazardous areas" myth. You don't need fuses identified for Division 2. Here's the code background on using fuses in Class 1, Division 2 locations. I'm assuming you already know the area is Class 1, Division 2, Group B/C/D, and some temperature code (assuming T3). Referencing 2011 NEC:

Section 500.8 (A) - Suitability. Suitability of identified equipment shall be determined by one of the following:
(1) Equipment listing or labeling
(2) Evidence of equipment evaluation from a qualified testing laboratory or inspection agency concerned with product evaluation
(3) Evidence acceptable to the authority having jurisdiction such as a manufacturer's self-evaluation or an owner's engineering judgement

It looks like you're trying to use option (1), which is the most black and white but also the most restrictive. It costs manufacturer's a lot of money to have UL, ETL, CSA, FM, or another lab test their product. In most cases by the very nature of the product it is self-eveident that it will be suitable for Class 1 Div 2 - that's where 500.8(A)(3) comes in.

Assuming you are a consultant and the owner isn't willing to make any judgements, we'll proceed with listed or labeled equipment only that meets the code without any interpretation.

Article 501, Section III - Equipment
501.105 - Meters Instrumentation and Relays

501.105(B)(5) Fuses. Where general purpose enclosures are permitted in 501.105(B)(1) through (B)(4), fuses for overcurrent protection of instrument circuits not subject to overloading in normal use shall be permitted to be mounted in general purpose enclosures if each such fuse is preceded with a switch complying with 501.105(B)(1)

This section right here should dispell any need for Class 1 Division 2 fuse blocks or fuses, because it's fairly cheap and easy to comply with 501.105(B)(1):

501.105(B)(1) Contacts. Switches, circuit breakers, and make-and-break contacts of pushbuttons, relays, alarm bells, and horns shall have enclosures identified for Class 1, Division 1 locations in accordance with 501.105(A).
Exception: General purpose enclosures shall be permitted if current-interrupting contacts comply with one of the following:
(1) Are immersed in oil
(2) Are enclosed within a chamber that is hermetically sealed against the entrance of gases or vapors
(3) Are nonincendive circuits
(4) Are listed for Division 2

This gives you a few options, we use each of these options depending on the particular application:
1. Mount an "explosionproof light switch" for the main incoming power next to the NEMA 4X instrument enclosure. We use this approach for our wireless tank gauging system tankside monitors. The box contains a wireless radio, an interface between the radio and 4-20 mA loops, and a 120VAC to 24 VDC Class 1 Div 2 power supply. There are five fuses in the box in Shawmut USCC1I holders - a 120V main fuse, a 24VDC main fuse, 24VDC branch fuse for the radio, and two 24VDC branch fuses for the two loops. This approach works because any time we need to change one fuse, it doesn't hurt anything to kill the power to the whole box. The other time this works is even if we can't kill the main power and need to change a fuse, we can take a gas test and write a hot work permit which allows us to do spark-producing opeartions like opening a switch, drilling a hole in the box, grinding, welding etc. The "explosionproof light switch" is a Crouse-Hinds EDSC2129 - go to www.crouse-hinds.com and type the part number in the search box.

2. If you can't kill the main power to the box and need multiple individual disconnecting switches, you could use 30 MM 2 position control switches with sealed contact blocks. We use Allen Bradley 800H-HR2AP switches in this application. These switches are NEMA 4X rated themselves and can be mounted in NEMA 4X boxes in Division 2 areas using 501.105(B)(1) Exception 2. I think these blocks also carry a Division 2 listing so they meet 501.105(B)(1) Exception 4 as well.

All of this being said, for the Weidmuller fuse block to be actually useful it would have to have a disconnecting means ahead of the fuse that is compliant with 501.105(B)(1). This fuse block looks just like an other instrument fuse block from Weidmuller, Phoenix Contact, Allen Bradley, etc. so I doubt it has a disconnecting means suitable for Division 2. This means some disconnecting means compliant with 501.105(B)(1) is still required upstream of the so-called Class 1 Division 2 fuse block. This is what I mean by the "certified for hazardous areas" myth - the product is listed or labeled for Class 1 Dvision 2, but you have to take the same measures to make it usable as you would with any non-listed block. It's a marketing technique only - save your money and increase your options - buy any instrument fuse block you want, put in a local sealed disconnect switch on the main incoming power to the box, and put a sign on the box indicating that the fuse block is only to be operated with the power off or with a hot work permit.
thanks for the amazing reply. Here in the great white north the CSA code 18-164 states;
Where fuses are used in class1 zone 2 locations for the protection of motors,appliances,and portable lamps
(a) a standard plug or cartridge fuse shall be permitted to be used if placed within an explosion proof or flame proof enclosure.
(b) a fuse installed within a general purpose enclosure shall be permitted provided that the operating element of the fuse
(i)is immersed in oil or other suitable liquid
(ii)is enclosed within a hermetically sealed chamber;or
(iii) is non indicating, filled, current limiting type.
I haven't been able to find anything on having an Ex switch upstream of the instruments.


Thanks to all. This is very informative. I have a similar application i'm trying to deal with.

As an alternative to comply with 501.105(B)(5), would it be acceptable to install a DIN rail mounted sealed circuit breaker directly feeding the fuseblocks? In other words, is a breaker technically considered a switch?

I would be interested to know what the purpose of 501.105(B)(5) is. Does anyone have any input?


Senior Member
(iii) is non indicating, filled, current limiting type.
This is pretty easy to do. The Bussmann Low Peak line of fuses are current limiting and powder filled, you just have to make sure they don't have the indicating window that turns black when the fuse blows. The smallest is the Class CC #LP-CC-X, where X is the amp rating.
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