To fuse or not to fuse???

[teamtexas]

I've got a brand new set of 203v's and I'm trying to determine if I should install a fuse on the line from the power supply to the drives? If I should fuse this, do I need to install a 470uf 100vdc capacitor across the drive terminals 1 and 2?

Dan

[Mariss Freimanis]

Fuse the AC input to your power supply. That protects you should the power supply fail. Otherwise, the G203V needs no additional fusing because of its internal ultrafast-blow fuse.

The G203V doesn't absolutely require an external 470uF/100VDC cap but it's nice to install one anyway, especially for larger motors.

Mariss

[M100]

Hate to disagree with you Mariss but I just have to on this point.

Any fuse or other protective device between the power supply and the drive is purely there to protect the wiring and the power supply, the drive requirements and their internal fuse even if ultrafast is completely irrelevant. Other external influences such as a dropped screwdriver or a damaged conductor, or a stray piece of swarf can short circuit the power supply in a heartbeat, particularly in a prototype installation.

*If* the wiring and other components are capable of staying within their thermal limits in such circumstances then no fuse is required, however a suitably sized fuse or thermal magnetic circuit breaker wouldn't go amiss because sh1t sometimes happens and hot pvc stinks. Something that will kill the secondary supply within a second or so is infinitely preferable to cooked wiring / transformers and a fuse on the AC side can be slow especially if the rating is tweaked to stop it blowing on inrush current.

[Mariss Freimanis]

I theory then every single wire coming from the supply should be fused. That is not a bad idea if someone has a lot of fuses, fuse holders and a place to put them all. If there is only one fuse then it should be put to best use, that being in the AC input circuit. Overload the DC output? The fuse blows. Short the primary? The fuse blows.

Mariss

[M100]

Coming as I do from a 30 year background in high voltage transmission and distribution and dealing with high energy systems such as 50v and 110v battery banks that use hundreds of kg of lead in their cells, with busbars 200mm wide and 20mm thick and with many low (sometimes sub 1A) current devices connected to them might affect my attitude with respect to automation wiring. In the power transmission and distribution field everything is fused or protected at the appropriate level based on the downstream cabling and to a lesser extent the components, one fuse on the battery, one on the charger, one on the feed to each rack, one to each subrack, one on the feed to each individual circuit board with multiple fuses on each individual circuit board.

This philosophy extends in some respects to AC wiring in the UK where we have a main fuse or MCB upstream of the distribution board, then individual protection at the distribution board sized appropriately for the fixed building wiring, then have a fuse in the mains plug to protect the flexible cord, (sometimes also with a fused mains inlet on the equipment in the case of IEC connectors), the transformer may also have a thermal fuse to protect against a long term overloaded secondary and then the secondary might be fused on a single or multiple basis to protect secondary wiring. Sometime these secondary fuses might be self resettable (Tyco Polyswitch) fuses.

Protecting every single wire on the LV side of in a stepper/servo drive assembly can sometimes be realistically achieved by one secondary fuse prior to a star point - but it usually takes two if you have a breakout board or additional I/O like a PLC. If you have a fault on the transformer, or the bridge rectifier or capacitors then the primary side fuse should provide the required protection.

So three fuses in total, in total taking less than a couple of inches panel space.

I'd *never* just fuse on the primary - a 230v 500VA transformer with 25v secondary feeding four Gecko 203V's and a breakout board would need to be fused with a minimum of a 2.5A, and possibly even a 3.15A antisurge fuse to avoid it blowing on power up. The drives could realistically each be wired in 1.0mm2 (32/0.2mm2) which is rated at 6A at 70 deg C.

Have a drive, or the wiring go short and the infeed at 25V, 20A will overheat the wire, which is adequately sized for normal operation and the primary sized fuse might do absolutely nothing - ever.

Fuse the feed to the secondary star point at 20A quick blow and the secondary wiring will survive and no magic smoke will escape.

[Mariss Freimanis]

My assumption is the four G203Vs are wired using "star" distribution. One +supply wire and one return wire per G203V. Each G203V has an internal fuse going from the +supply terminal to the internal circuitry.

Mariss

[fatal-exception]

I didn't bother fusing my latest g320 system, just make sure no sh__ can get into your controller cabinet. Neither of my g203 systems have ever blown their 5 amp fuse, and they had plenty of chances to do so.

Nobody can seem to answer the fuse issue for us 'non electical' guys. Maybe we should stop answering the mechanical questions, or create such a smoke cloud that they walk away confused as we often do.

Paul

[M100]

Nobody can seem to answer the fuse issue for us 'non electical' guys.

You should ALWAYS fuse (or use mcb's) to protect the downstream items whatever they are. The fuse/shutdown protection in the stepper / servo drivers should, but might not always suffice for the wiring from the drive to the motors but that leaves a huge amount of upstream wiring, the transformer etc completely unprotected.` Fusing ONLY the transformer primary can conceivably lead to overheating of correctly sized wiring on the secondary under short circuit conditions hence why fusing ONLY on the primary is a bad idea.

The wiring and all devices connected to it, all the way from the electrical inlet to the building to the point at which it enters the stepper / servo drivers should be protected. The fixed wiring in the building, if it meets wiring regulations/electrical code should be appropriately protected which just leaves the section from the socket on the wall to the point at which the wiring physically enters the (hopefully Gecko) driver module.

1) Fuse the mains supply as it enters the enclosure to cater for a failure on the primary side of the transformer either to itself, or to earth.

2) Fuse (the same one as above) the mains supply as it enters the enclosure to cater for a failure of the transformer secondary either to itself or to earth.

3) Optionally fuse the secondary of the transformer wiring as close to the transformer housing as possible to protect against capacitor failure, rectifier failure, or wiring failure (the mains side fuse might *sometimes* suffice for these failures although it is by no means certain)

4) Fuse the output from the power supply just before the secondary star point where all the drive wiring is commoned to protect the wiring from the star point to the drives themselves. This fuse might also protect things like e-stop wiring, guard interlocks,

From the replies that Mariss is giving there is either a difference of opinion here or, (and I'd be very surprised if this is the case) a lack of understanding of why, how and where you protect. I know my philosophy would be accepted within industry, costs next to nothing to implement and critically stops smoke from escaping

Of course you could put no fuses in and hermetically seal your drive enclosure, the smoke would still be enclosed but not precisely where it should be.