Finding HRC fuses for a safe, interim electrical installation of disconnect switch and breaker panel

[Bruce404]

I am having trouble finding in Chiang Mai the parts to allow a modern High Rupture Capacity (HRC) fuse (which may be known by other terms, as well) that will allow a new 100-Amp Schneider/Square D fusible safety disconnect switch to provide protection for the system by only an interim 50-A HRC fuse.

The project is on now-vacant land, although it had crude, ungrounded, single-phase service with 16mm² wires. The old aluminum, single hot and neutral cables will be re-used now in a 50-Amp, 1-phase setup until the entire system can be upgraded in a year or so to 4-wire, 3-phase service meeting advanced international standards (e.g., European/North American/ANZ).

This will likely require 25mm², 35mm² (or thicker?) cables from a new 3-phase meter, depending on the demand to be estimated for a future house and various outbuildings. The interim installation is for outdoor security lighting, a water pump, and power for expected construction activities (e.g., welders, cement mixer motors, concrete vibrators, etc.).

The new equipment, now in the process of being installed on an interior boundary wall of the property, is sized to be reusable in the future 3-phase, higher-amp system, either as main switches/panels, or as subunits. It includes a Schneider / Square D 3-phase circuit breaker panel box (100A rating, 12 fuse slots, model QO3-100EZ12G/SN), for which only its black phase will be wired up now.

The problem is that the Schneider/Square D fusible safety disconnect switch (100A-rated model H363RB), picked up at Home Mall in Chiang Mai, seems not to accept the sizes of available 50A box-style or bladeless-cylindrical HRC fuses available in Home Mall or Global House (such as some box-shaped or bladeless cylindrical ones) that would come close to meeting modern international standards to stop 200,000 A (200 kA) or even 300 kA fault currents that might occur and destroy our electrical system if a short circuit were to occur, or something happen upstream in Provincial Electricity Authority (PEA) equipment.

For example, the default position of the disconnect switch (Schneider1-etc. photograph) has approximately 155 mm between its clamps to accept the body of a flat-bladed-type fuse, although there is plenty of airspace to extend beyond their outer distance of ~200 mm. When moving the lower fuse holder to the available upper position (Schneider2-etc photo), these distances become ~75 mm to clear a fuse body, and ~115 mm of the clips' outside distance.

Even turning the lower fuseholder upside down and using the original, lower mounting holes (demonstrated but not actually shown in the Schneider3-etc photo), the distances become even shorter (~62 mm for the fuse body to clear, and ~106 mm of outside clip distance). (Surprisingly, even thus jury-rigged, the lower fuseholder fits securely, without interference from the positioning "bumps" in the rear wall of the box. Running the sole black "hot" wire upwards from the lug should not be a problem, as the conduit to the adjacent breaker panel is the blue PVC fitting at top).

Schneider itself does not provide much help at its page about this switch, where among FAQs is a description of possible fuse classes (H K J R) that can be installed (but not necessarily when downsized to 50 A).

An obvious solution would be to find so-called "fuse reducers", which paradoxically "extend" the length of a too-short fuse, to fit my wider blade clips, or to convert an unbladed fuse into a bladed one, as shown in some attached photos of Cooper / Bussman / Littlefuse adaptors.

Several threads on ThaiVisa in 2010, with thoughtful input from "Crossy" and others, indicated there are among ThaiVisa followers a number of knowledgeable, professional-grade, ex- or current electricians who might have advice to offer. One lesson I took from those threads is that one should not rely on the PEA to install such protective fuses upstream of our meter. Thus, the reason for the rather pricey safety disconnect switch being installed just upstream of our circuit-breaker panel (and about 75 meters downstream from the old PEA meter across the street).

Does anyone know where in Chiang Mai one can get the desired 50A, 20kA or higher HRC fuses that might fit, and/or the adaptors to extend their length sufficiently for our switch box? Due to travel plans, mail-ordering from Bangkok is not an option at this time, as our hired electricians and I both want to get the job finished soon, and they seem unaware of such technical matters.

Another problem is that nobody seems to have in Chiang Mai single-phase, 16-Amp Residual Current + Overload Breaker/Ground Fault Circuit Interruptor (RCBOs/GFCIs) devices with their trip current at a more practical 30 milliamp (mA) current. Given the quality of outdoor extension cords I have seen, the 10 mA breakers I can find are likely to be tripping all the time, frustrating contractors trying to get their work done.

I don't want to encourage them to tie their extension cords into electric lines upstream of such life protection, a common practice it seems. Any suggestions for a quick source of 30-mA-tripping RCBOs/GFCIs to fit a conventional Schneider/Square D panel?

Thanks!

[Support]

Moved to the Electrical forum

[Crossy]

Sorry I can't be of any help I suggest Ebay will be your friend.

It strikes me as odd that the place that supplied the breaker cannot also supply the fuses (even if you temporarily install bigger than you want to get the supply on?).

I doubt very much that your supply has a PFC of anything like 200kA, ours measures as nearer 2kA.

DIN mount RCBOs of 30mA 10A are readily available, any reason you chose to limit your choice by specifying a SquareD CU, ours are ABB with DIN mount everythings?

[Bruce404]

Sorry I can't be of any help I suggest Ebay will be your friend.

It strikes me as odd that the place that supplied the breaker cannot also supply the fuses (even if you temporarily install bigger than you want to get the supply on?).

I doubt very much that your supply has a PFC of anything like 200kA, ours measures as nearer 2kA.

DIN mount RCBOs of 30mA 10A are readily available, any reason you chose to limit your choice by specifying a SquareD CU, ours are ABB with DIN mount everythings?

Thanks for your response to my posting. The problem is I am downsizing the fuse to 50A from the default 100A rating of the disconnect switch, and want to use a highly-rated HRC type fuse, not a no-name one with no rating (or a low rating like up to 10,000 amps [10kA]) for fault-current protection.

Home Mall in northern Chiang Mai where the disconnect switch was bought has long 100A bladed, cylindrical fuses that fit its default position of the lower fuse holder, as well as shorter 50A ones that might fit its upper position. But these breakers are quote old-fashioned looking, with absolutely no specifications of what their ratings might be (if any) for fault-current limiting. I doubt it would be in the minimum 200 kA range now standard in many developed countries.

Global House in southern Chiang Mai has similar-looking ones from Eagle Electric, a nostalgic old brand made in Long Island, New York. But it, too, has no specifications other than overload amperage, and appear to have been manufactured ages ago.

Global House does have in stock modern-looking box-shaped HRC fuses (similar to the attached photo "Siemens-HRC-Frses.jpg", but not the same brand), and bladeless cylindrical (type R?) fuses (like the example photo "Littelfuse-50A-classRK5-fuse_etc.jpg"), both of which have high fault-limit ratings. But the problem is getting them to fit the existing fuse-holder clips, or getting adaptors for them to do so.

About the RCBOs, neither Global House and HomePro in southern Chiang Mai stock any compatible brands of the desired ones whose Schneider model numbers end in "30", indicating a 30mA trip rating (see attached table from a Schneider catalog: "SCHNEIDER-RCBOs.jpg"). Global House and HomePro only carry the 10mA-rated ones.

So any suggestions where one can pick up in Chiang Mai fuse "reducers" or adapters, as well as RCBOs with 30mA trip ratings, would be welcome. The alternative is to use now whatever can be found locally, and then replace them with safer items when they can be obtained overseas or from Bangkok.

Thanks, again.

[Forkinhades]

^ I have never seen 200kA rated HRC fuses.

Even in the UK the Main HRC fuses are only 50kA, and by calculation a 3 phase fault will only generate 40kA @ 10milliohms

The links you show are for 'k' curve which is for specialist equipment.

Do you have a better picture of the fuses, which show the kA?

RS Thailand will do your 16A RCBO @ 30milliamps

EDIT: BS88 are 80kA

[Forkinhades]

http://th.rs-online.com/web/p/residential-rcbos/4183468/

not cheap though!

[Forkinhades]

http://th.rs-online.com/web/c/?searchTerm=hrc+fuse&sra=oss&r=t

just a quick search came up with this

[Crossy]

http://th.rs-online.com/web/p/residential-rcbos/4183468/

not cheap though!

Problem is he has a SquareD CU, not DIN mount

[Bruce404]

Finally getting around to an update as the Original Poster of this thread.

I temporarily installed in a single phase of the Service Disconnect (SD) a 100-Amp High Rupture Capacity (HRC) Bogenfuse rated at 120,000 amps for fault-current-limiting purposes, found at Global House, Chiang Mai (see image IMG_6172rotated.jpg). There was no desired 50-amp version for the 16mm² "recycled" wires. But since the panel downstream has a 50-amp main breaker at that rating, it should be fine to protect the equipment. The fuse in the Service Disconnect is primarily to protect from fault currents in case the PEA does not do the job for my neighborhood.

This Bogenfuse eurostyle (DIN?) fuse did not properly fit the Schneider/Square D Service Disconnect fuse-holder, so its blades had to be filed down for the narrower openings in the SD. Subsequently, at a Home Depot in the USA, I was able to find a Bussman brand of HRC fuse rated even higher for fault-limiting, at 200,000 amps (see image IMG_6222.jpg), which slipped into the DS perfectly (IMG_6432rotated.jpg) upon its replacing the jury-rigged, temporary Bogenfuse. It, too, though, was overrated at 100 amps for my temporary, construction-phase wiring with only 16 mm² wires from the meter and service drop ("cobra") at the street.

The overall installation is seen in images IMG_6179.jpg and IMG_6171.jpg. As per the U.S. National Electrical Code, only the SD has its neutral line bonded to an earth/ground (see ECMweb-Code-Basics-BondingNeutral_etc...jpg image), but NOT again in the breaker panel (ECMweb-Code-Basics-Improper-Neutral_etc...jpg).

The Schneider breaker panel has only two RCBO ("GFCI" in the USA) circuit breakers (IMG_6173rotated.jpg) on its black phase, supplying a utility box with outlets for use during future construction, as well as a switch for an overhead, photo-celled utility night light at the top of the steel pole (which used to carry power to a decaying hut).

I was not around when the local "electricians" decided to mount the panels directly behind this existing pole, instead of to the side. So it was easier just to construct the roof around the pole than to pull the boxes down from the wall and move them over a bit. Although the SD is weather-rated, the breaker panel and utility box are not, thus the need for the roof. Someday, most of this will be moved and recycled inside a proper building, where the additional two blue and red phases will be wired up, as well.

Only problem noted to date was that one of the 16A or 20A RCBO/GFCIs (cannot remember which) was rated for 10mA electrocution protection, and was flipping off in the rainy season, suggesting a small current leak somewhere, perhaps at the pole. No problem when it was replaced with a 30mA one. But it is now the dry season. So we'll have to see what happens when the humidity next rises.

That's all for now. Safe wiring to y'all ...

[Crossy]

I think you're well over-specified, but that's up2u.

I suggest you read this PEA document (OK look at the drawings) http://www.crossy.co.uk/Handy%20Files/groundwire.pdf

It is important that you follow the Thai requirements for grounding, wire sizes and particularly the Neutral to Earth connection (MEN link) if you don't do it the correct way you will not pass the PEA inspection to get a permanent supply connected.

[IMHO]

I think you're well over-specified, but that's up2u.

I suggest you read this PEA document (OK look at the drawings) http://www.crossy.co.uk/Handy%20Files/groundwire.pdf

It is important that you follow the Thai requirements for grounding, wire sizes and particularly the Neutral to Earth connection (MEN link) if you don't do it the correct way you will not pass the PEA inspection to get a permanent supply connected.

Are you sure MEN is now standard country-wide?

[Crossy]

Are you sure MEN is now standard country-wide?

Good point IMHO, I forgot my usual rider regarding MEN i.e. ensure your area has it implemented before linking anything, if unsure don't.

It's supposed to be implemented on all new installations (along with grounded outlets and front-end RCD protection) but there are plenty of villages which are still TT (or even IT). The PEA "Groundwire" doesn't even mention TT.

[Bruce404]

For those perplexed by the jargon and abbreviations, this page nicely explains the terminology and compares the pros and cons of differing electrical codes, including those of Europe, Australia/New Zealand, and North America (USA/Canada):

http://en.wikipedia.org/wiki/Earthing_system

In the system illustrated, there are no metallic conduits nor designated earth/grounding wires connecting the distribution point at left (Service Disconnect [sD]) to the circuit-breaker panel board in the center.

However all components are sharing a common earthing/grounding rod. If that rod ever fails to make a good connection to earth, or there is some damage to a neutral line in the system, I suppose it is possible for that "objectionable parallel path of neutral current" to occur along the earth/ground wiring, as illustrated in the second cartoon.

If indeed the Provincial Electricity Authority in semi-rural Mueng Chiang Mai is following the Australian/New Zealand standard of Multiple-Earth-to-Neutral (MEN) connections in a TN-C-S system, then perhaps such a shared, single earthing/grounding rod would be a problem.

So I wonder if the neutral wire in the SD should have its own, exclusive earthing/grounding rod, even if just a meter or two away from another one for the metal frames of the SD, circuit-breaker panel board, and utility box, as well as the earth/ground wiring to all "downstream" utility outlets?

[Crossy]

The implications of an open neutral is one of the reasons TN-C-S (with or without MEN or PME) was not used in the UK until relatively recently and then only as a cost saving exercise when the ancient armouring on the distribution network (which was providing the earth in the TN-S system) started failing leaving homes with no reliable earth.

The way to do it here is to follow the PEA documentation if you're sure MEN is implemented (look for a neutral ground on every 3rd pole), if unsure leave it as TT.