Hager mcb

[Iona222]

Seen a consumer unit hager today, was old, the mcb had a little door on it, I opened one and it had a 3a plug fuse in it. Are they for storing stuff. Whats the low down with them? Cheers.

 

[Dartlec]

You mean these? Still available, but rare in domestic usage now. Flat I was in today still has them for the off peak circuits (Memora 2000 brand). Easier to replace than fuse wire, certainly - though not always that easy to find off the shelf...

I believe there are occasions in commercial/industrial scenarios where fuses have an advantage over MCBs still (not sure when though).

 

[Iona222]

You mean these? Still available, but rare in domestic usage now. Flat I was in today still has them for the off peak circuits (Memora 2000 brand). Easier to replace than fuse wire, certainly - though not always that easy to find off the shelf...

I believe there are occasions in commercial/industrial scenarios where fuses have an advantage over MCBs still (not sure when though).

Ye them, is it for storing fuses. Seems odd.

 

[Dartlec]

Ye them, is it for storing fuses. Seems odd.

Nope, they are just fuse carriers - the fuse is the protective device, just as fuse wire was. Still valid in BS1761 in suitable circumstances - BS3036

Unless you mean the spare cartridge box - which looks like it could be fitted into a unit to store spare fuses for the remaining ways?

 

[loz2754]

They're not plug fuses, but BS1361 cartridge fuses for use in consumer units, still in common use.

 

[westward10]

Shouldn't have a 3A fuse in it they are BS1362 not BS1361.

 

[Dustydazzler]

the old mem fuse boards with the dumpy fuses still loads of them in my area , some even have a front up rcd as the main switch

I once pressed the test button on one and it went bang blowing up the internaLs and the switch went floppy like a month old lettuce leaf

 

[pc1966]

You mean these? Still available, but rare in domestic usage now. Flat I was in today still has them for the off peak circuits (Memora 2000 brand). Easier to replace than fuse wire, certainly - though not always that easy to find off the shelf...

The rewirable fuses came first in electrical history, and newer BS3036 versions have continued in use still today, but they have several big down-sides:

• Replacing wire needs some skill, and often the public lacks that (especially as often it was the 5A lights circuit that went, at night, so dark and trying to fiddle with the little wire-retaining screws)
• Following from the above, folk would often put in the wrong wire, either by mistake or deliberately to "stop it blowing so often", with potentially serious effects.
• Inserting or withdrawing a fuse on load can end very badly, so again a bit of skill or sense to follow that warning is needed.
• Those fuses have very limited breaking capacity as nothing specific to quench the arc that forms when the wire blows.

Quite early on the HRC fuse was developed with the wire in a ceramic tube and filled with arc-quenching sand. Just think how far back BS88 originated from the number alone!

These HRC fuses solved the breaking limit for most situations, upping from a couple of kA to hundreds of kA as needed, and as a plug-in (or bolt in) device were a little simpler to change. The problem of interchanging fuses in the domestic (low or non-skilled user) case was sort-of tackled by the likes of BS1361 where different fuse ratings have different body sizes, unlike BS88 where you get a big range in an identical body.

But still the fuses have two real issues, especially for domestic use:

• Changing under load (or using to isolate) can be dangerous
• If one blows often nobody has a spare, and its at night and shops closed.

So they had a short period of popularity from the workhorse of BS3036 until the arrival of reasonably priced MCB, at which point you really would not use a fuse for any domestic CU (though we still have them in 13A plug and FCU, of course).

I believe there are occasions in commercial/industrial scenarios where fuses have an advantage over MCBs still (not sure when though).

The HRC fuses like BS88 has some advantages over MCB and MCCB that make them still a popular choice in an overall system design:

• In general, fuses have much better energy-limiting capabilities at high PFC than MCB or MCCB. Good for cable adiabatic, as well are reducing the risk of arc-flash / arc-blast injuries to anyone working live.
• Due to the smooth time/current curves, fuse-fuse cascades can achieve total selectivity at ratios of 1.6:1 to 2:1 in a distribution system.
• When feeding a MCB, a suitable fuse can still achieve sufficient selectivity in practice (often at several kA fault, where as end of circuit PFC might only be a kA or so) as well as protecting the MCB from massive PFC, so long as the fuse is starting to break and thus energy-limit at the upper range of MCB safe operation (typically 6-10kA)
• Fuses are much cheaper than MCCB. So if you don't need some of the fancy adjustable features of electronic MCCB, or its use as a means of isolation on-load, you can have a better and cheaper solution for high current distribution/protection using fuse s (for example, the Ryefield boards, or a bus-bar chamber with a few fused-switches if you need isolation/switching on load as well)

Here is an educational/advert video comparing fuses and MCCB, while it is biased towards fuses in some ways, it serves to illustrate some of the above points quite graphically:

 

[telectrix]

that's 5 minutes of my (now) limited time on earth that can't be recovered. beam wake me up Scotty.

 

[pc1966]

that's 5 minutes of my (now) limited time on earth that can't be recovered. beam wake me up Scotty.

Good job you didn't watch the video as well!

To be fair, it is both more entertaining and has a better plot than some Hollywood films I have wasted an hour and a half of my life watching...

 

[freddo]

Here is an educational/advert video comparing fuses and MCCB, while it is biased towards fuses in some ways, it serves to illustrate some of the above points quite graphically:

I still believe parts of that video are fake, as I did 3 years ago! The explosions cool though.

 

[pc1966]

I still believe parts of that video are fake, as I did 3 years ago! The explosions cool though.

Which bits?

 

[freddo]

This for one:

 

[littlespark]

You been wearing that head for 3 years? Bloody hell it must be stinking…. ?

 

[Moley]

You been wearing that head for 3 years? Bloody hell it must be stinking…. ?

I would like to see the look on his customers face when they open the door to him ?