fused pilot lights?

[lowvoltman]

Would a 480v transformered pilot light require fusing? I believe the lamp itself is 6 volts. If so what size?

 

[petersonra]

I do not believe the light itself requires fuses.

I do think that in general, the conductors feeding the light do.

 

[templdl]

As I recall the pilot light assembly has a big resistor mounted to the back of it to drop the voltage and must be used with a specific bulb.

 

[Twoskinsoneman]

Would a 480v transformered pilot light require fusing? I believe the lamp itself is 6 volts. If so what size?

Does transformered pilot light mean it is transformed from 480 down?

 

[Smart $]

Would a 480v transformered pilot light require fusing? I believe the lamp itself is 6 volts. If so what size?

As already stated, the light itself does not require fusing. Actually, it is in a sense a fuse itself (assuming incandescent).

I believe the true question is whether the circuit needs fused. That's going to depend on details you did not provide. Need to know at the very least transformer primary and secondary voltages, no. of phases, no. of wires, output and/or class rating, ocp of primary, secondary wire size, and anything else pertinent, such as located in an industrial control panel...

 

[broadgage]

I doubt that a 6 volt pilot lamp worked from a 480 volt supply uses a series resistor to drop the voltage.
Presuming that the 6 volt lamp uses 0.3 amp, a very common rating, then the resistor would have to disipate about 140 watts, most unlikely.
Even if the lamp is only 0.1 amp, then the loss in the series resistor would still be nearly 50 watts.

I would expect that a transformer is used, perhaps built into the lamp holder.
With a transformer efficiency of 50% and a 6 volt 0.3 amp bulb, that would give a total use of about 3.6 watts.
Transformer lampholders for 415 volt supplies are used in the UK, and I would expect that similar products for 480 volts are used in the USA.

A control panel might be considered an appliance and therefore not covered by the NEC.
It would be good practice to protect the transformer lamp holder and the wires to it by a fuse, unless the circuit to which it is connected already has a fairly small OCPD.

 

[Jraef]

If it is a 6V lamp, it is a transformer type pilot light, there is no other 480V style available. In those devices, you can connect a PILOT LIGHT directly to a circuit without another fuse, the transformer itself is considered "self protected", which just means if there is a short circuit, the windings open up (and self extinguish) as fast as a fuse. This allows them to be used in applications such as Blown Fuse Indicators or Power On indicators on the load side of a disconnect or circuit breaker.

However applications other than those two mentioned above are also going to typically involve some other sort of pilot control device; a push button, selector switch, pressure switch, relay contact etc. THOSE devices will have pilot duty ratings. So for example of a device is rated NEMA A600, it can make 60A, break 6A and carry 10A continuously. So that means it MUST be fused for 10A max. be careful though, a lot of IEC pilot devices and realys have a B600 rating, which means a 5A fuse and some small reed relay type devices may be 3A or 1.5A max. You really have to study every device in the control circuit before selecting the fuse size.

Just FYI as you are doing that, look carefully at the VOLTAGE rating of any added pilot devices as well. A lot of things are only rated 300V max (i.e. NEMA A300 or B300) so you cannot use them at all on a 480V line voltage control system. This gets overlooked a lot lately because people are not used to 480V control circuits any more.

 

[lowvoltman]

self contained class 1 div 2 pilot light

self contained class 1 div 2 pilot light

It's a self contained unit with transformer. 6.3 v bulb 150 ma with 380-480 primary. we are using it to just signal a circuit is energized. Would that be covered in the NEC ? If not we were thinking of fusing it to just protect the rather expensive pilot light. What fuse size would be appropriate? Not much load to speak of. thanks!

 

[Jraef]

It's a self contained unit with transformer. 6.3 v bulb 150 ma with 380-480 primary. we are using it to just signal a circuit is energized. Would that be covered in the NEC ? If not we were thinking of fusing it to just protect the rather expensive pilot light. What fuse size would be appropriate? Not much load to speak of. thanks!

The MAJOR problem with that is that if you fuse it, and the fuse blows, you will THINK the power circuit is de-energized when it is not, exactly the OPPOSITE of what you want! It doesn't need to be fused in that circumstance, I would not do it.

There may be a better product choice by the way, a "Voltage Vision" unit from Grace Engineered Products. It is designed specifically for this purpose and is UL listed for this, and it will cover all 3 phases or all incoming lines. They have also been accepted as valid for NFPA 70E indication without testing, meaning you don't have to suit up just to check to see if power is off. I've been using them everywhere lately.

Voltage Vision link

There is a Cl1 Div 2 version available if you click on the PDF links

 

[GeorgeB]

It's a self contained unit with transformer. 6.3 v bulb 150 ma with 380-480 primary. we are using it to just signal a circuit is energized. Would that be covered in the NEC ? If not we were thinking of fusing it to just protect the rather expensive pilot light. What fuse size would be appropriate? Not much load to speak of. thanks!

We had Allen Bradley 800T devices specified by several customers, and when the MCC was not equipped with a transformer or remotely powered, their 480:6.3 transformer lights were specified. I don't remember including them on any of our drawings ... we only did drawings when WE controlled the starters ... and looking back, the control circuit was probably locally fused with a small KTK type fuse (one? then, a pair today?)

 

[Smart $]

The MAJOR problem with that is that if you fuse it, and the fuse blows, you will THINK the power circuit is de-energized when it is not, exactly the OPPOSITE of what you want! It doesn't need to be fused in that circumstance, I would not do it.

...

Not fusing it may present a problem if it actually falls under NEC pervue. Connecting to a circuit that has higher-rated ocp than the connecting wires makes those wires taps, and then subject to tap rules. So either install in a manner that is NEC compliant or install at a location and or manner that is not subject to NEC compliance.

 

[petersonra]

You really have to study every device in the control circuit before selecting the fuse size.

Not so sure about this. I had this very discussion at length one time with a manufacturer's engineer. There is generally no requirement to protect any device with an OCPD. You do have to use them within their ratings. You do have to protect the conductors.

Just FYI as you are doing that, look carefully at the VOLTAGE rating of any added pilot devices as well. A lot of things are only rated 300V max (i.e. NEMA A300 or B300) so you cannot use them at all on a 480V line voltage control system. This gets overlooked a lot lately because people are not used to 480V control circuits any more.

Agreed on this one.