Mike Holt's Forum

480 volt fuse safety

JWinters — Wed, 16 May 2012 23:46:21 GMT

I saw these fuses in a 480 volt bus bar disconnect and the contact points of the fuses had small cracks around them. I cant seem to get an answer on the cause or if its a safety issue.

Arc Fault Circuit Breakers

mmcneill0003 — Wed, 16 May 2012 23:34:40 GMT

Article 210.12 Arc-Fault. List all the locations that Arc Fault Breakers are to be installed. Question: Does this article still apply to an addition added onto an existing house with standard breakers. Or is this addition covered under a grandfather clause. Can't find this information in the NEC. Thank you.

Is there a globe for pull string fixture or replacement fixture????

rt66electric — Wed, 16 May 2012 23:14:59 GMT

A friend ( police officer) is selling is OLD house and got Hammered by the hard-ball home inspector. It is mostly standard stuff. ungrounded/reversed recepts etc. The closets have the standard pull-string porcelin base fixture. Is there a pull-string Fixture with some sort of globe?? I would like a cheap easy fix without having to add a switch in an old house?? It does not have to work well, just pass inpection??

Would it pass inspection to blank off the light fixture? Is it required to have light in a small closet? If so what is the maximum size of a closet not required to have a light.

I feel like a lawyer, which side is paying me? Both answers are correct/legal. If your are buying a house---everthing must be updated and pretty, rewire thewhole house. If you selling, then, everthing Is FINE -- OK according to code at the time of construction.

RMC over roadway

ScottLund — Wed, 16 May 2012 22:59:20 GMT

Does table 225.60 apply to conductors in a raceway? What is the required clearance over an industrial driveway for 480V conductors in RMC?

Changing HazLoc light fixture from HPS to self ballasting lamp

fbhwt — Wed, 16 May 2012 22:31:38 GMT

I have been asked to repair some haz/loc (explosion proof) light fixtures, these fixtures are 150w HPS, I am new to the shop and was told to ask the other electrician in our shop if we had any lamps and ballast. He told me he has been changing these to self ballasting lamps that are close to or of equal wattage. I have never done this and would think that it would not be allowed if this fixture was certified as a 150w HPS

Emergency and Exit Lights

timm333 — Wed, 16 May 2012 22:26:09 GMT

I understand that if a building is open to general public, then emergency and exit lights are required by NEC.

Our building is open to general public during the day and not open to general public during night, do we still need the emergency and exit lights?

NEC 220.87 Multiple Loads

Tom Sawyer — Wed, 16 May 2012 21:49:36 GMT

Currently three generators are providing power to three different loads on the property. None of the three loads are connect together. We are replacing the generators with all PG&E. When doing a 30-day load study on each generator, do we use the peak average power over the 30 day period regardless of synchronicity or do we use the peak average power that represent the highest total power during a given synchronized time?

For example:

Gen 1 = 100 KVA (peak apparent power) at 5:15 PM
Gen 2 = 25 KVA (peak apparent power) at 2:00 PM
Gen 3 = 74 KVA (peak apparent power) at 9:15 PM

Total peak power = 194 KVA x 1.25 = 242.5 KVA for the service.

OR

Gen 1 = 100 KVA (pap) at 5:15 PM
Gen 2 = 10 KVA (ap) at 5:15 PM
Gen 3 = 14 KVA (ap) at 5:15 PM

Highest total peak power for a synchronized time = 124 KVA x 1.25 = 155 KVA for the service.

NM in PVC Conduit, on Roof

Bill Annett — Wed, 16 May 2012 21:11:37 GMT

Did an inspection today where the contractor ran NM cable from a panel on the first floor thru the second and third floor and then penetrated the roof with a short piece of PVC conduit ,then to carflex, to a disconnect for an AC unit. I told the contractor that NM could not be in a conduit outside because it is considered to be a wet location. I am home and left my code book in the office but I think that I cited code section 300.9. He said that if he strips off the jacket of the NM that he would be ok. I do not agree with that. His wiring method is NM. It started out as NM and has no splices so I can not see how it now could not be NM. AM I missing something? Any input will be appreciated. Code references will even be better.

I did not have a good day at work. On the way home I stopped and bought some Chinese food. The fortune cookie said � If you have a job without aggravations, you don�t have a job� The next time That I do not have a good day at work, I think that I will just get a Big Mac.

Thanks, I will check back to see your opinions. If I am wrong please let me know.

12.47kv overhead line

lilsparky — Wed, 16 May 2012 19:16:34 GMT

Ok here's today's question: there's a 12.47kv overhead line that feeds into a 500 kva 12.47kv - 480v outdoor transformer which feeds two facilities. Now we are upgrading this facility and adding in a fire suppression system that has to have it's own separate reliable power. I need to tap off the 12.47kv line at the pole to feed another 12.47kv - 480v transformer, however I only see 2 phases on the pole being brought down to the existing transformer. Is that correct? can I still tap this line?

Changing 20A plug to a 50A plug in order to use a 50A receptacle?

Gary386 — Wed, 16 May 2012 18:48:13 GMT

If I have a 20A device, with a 20A plug, is there any reason I can't change it to a 50A plug and use it on a 50A circuit?

In the extreme case, could I wire a clock (very low amperage) to a 50A plug and use it on a 50A circuit?
If the answer is no, then how is it OK for an electric range with a 50A plug run the built-in clock?

I know that it is OK to run a very low amperage night light on a 20A circuit. I understand that neither the night light nor clock in my examples are protected by the circuit breaker, but is this against code?

Formula to figure out the cooling time required for xformer loaded above nameplate?

tortuga — Wed, 16 May 2012 18:48:01 GMT

To all you EE's out here:
I am doing a little research on transformer loading above nameplate rating.
I am looking for formulas to figure out the cooling time required for xformer loaded above nameplate.

In this interesting thread i stumbled across a interesting quote :
http://forums.mikeholt.com/showthrea...mount+overload

Quote:

Originally Posted by jim dungar

Heat build up is what causes all transformers to fail (excluding short circuits). Theoretically, you could overload a transformer by 200% for 12 hours then turn it off for 12 hours, and it would last for its normal life expectancy. In reality it takes longer for a transformer to cool down then it does to heat up, so the period of loading would more likely be 200% for 8 hours followed by <50% load for 16 hours. There are formulas to figure out the amount of cooling time required based the ambient temperature and the actual loading profile.

I am wondering where I find some of these formulas?

(I have checked through some MFR data sheets, and looked through several manufacturers specs on sizing transformers and found some interesting stuff short of a formula.
I have glanced at a few dusty engineering text books as well.)

I found an article here however it is $225.
Thanks in advance for any formulas,tips, links or ideas etc.

BU bulb in a base down socket

cizzle21p — Wed, 16 May 2012 16:18:19 GMT

Why does this matter? We had to use a BU, PS 400W bulb in a lighting fixture that has base down socket. Any info would be great, just curious as to why it matters.

GROUNDING FOR UTILITY INTERACTIVE INVERTER?

mta145 — Wed, 16 May 2012 16:07:26 GMT

just installed a 100kw system with a utility interactive inverter. it is remotely located so at inverter we put 2 ground rods creating a DC grounding electrode system. Ran #6 cu to rods connected to the inverter DC GEC terminal. Inverter has integrated AC and DC disconnects. 690.47(c) says that i now have to bond the AC and DC elctrode systems together. So my question is since my AC grounding electrode system is at the main panel can i use my equipment ground in my inverter output circuit to bond the to systems together and if so what size does it have to be??

Thank you

MC CABLE & FINAL CONNECTIONS

horsegoer — Wed, 16 May 2012 16:07:01 GMT

If a spec reads that MC is only able to be used to make final connections to light fixtures is that considered the "whip/fixture tail" to the j-box and not all the branch circuiting for the lighting? Don't know if that can be interpreted in different ways? i would say that is just the tails/whips? Thanks.

Industrial Control Panels

Stan Hodges — Wed, 16 May 2012 15:34:51 GMT

I have an industrial control panel built in 2004/05 and it was built by a qualified electrician (but a non UL shop). We used the panel for a system and put it in storage and want to reuse the panel again for the same type of system (i.e. same controls, pumps, etc.). Can this panel be reused if it was not initially certified per the subject articles. Is
there an article in the NEC that grandfathers these old panels? Would it matter if a couple of mods were made to the system since 2005 � please note that the panel has been completely functionally tested for all operations/controls.