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#214970 - 02/17/15 10:48 AM Food warming table on GFCI circuit
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
I recently had a call to check a "food warming table" because the GFCI recpt. would trip when 2 elements(there are 4 elements total) were turned on. This is the type of table that only has elements in the bottom to keep the food warm and containers are set in over the elements. I looked at the nameplate and it pulls 2000 watts (16.7 amps). It was on a 20 amp breaker. I figured since it was pulling a little over the 80% requirement of the circuit that it needed a 30 amp. circuit so I installed a 30 amp. circuit and put it on a 30 amp. single pole breaker, still on a 20 amp. GFCI receptacle. It could now hold for 3 elements then would still trip out. I checked the elements to make sure one was not bad or the wiring was bad or wired wrong and found nothing.
I then thought the 20 amp. GFI might be maxing out for the 80% amperage. I got a 30 amp. GFI breaker and installed it. It still would hold for 3 elements but would trip when the 4th one was turned on. I called a kitchen equipment supplier and talked to them and they said their electrician took theirs off a GFCI and put it on a regular breaker. I had to do the same but am concerned why this would happen. Looks like it should be on a GFCI. It is located in a brand new Picnic shelter that was inspected. Where is sets is a kitchen like divider with counter space with no sink but on a cement floor. The receptacles around the counter are GFCI protected. Any ideas? Thanks

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#214971 - 02/17/15 11:12 AM Re: Food warming table on GFCI circuit [Re: sparkync]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5300
Loc: Blue Collar Country
Interesting.

I have installed several such 'steam tables,' and it never occurred to me add GFCI protection. I mean - who GFCI's a water heater?

I have had problems with elements going bad - often soon after installation. I attribute this to the place ordering 'used' equipment, or the elements being damaged in transit.

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#214972 - 02/17/15 11:57 AM Re: Food warming table on GFCI circuit [Re: sparkync]
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
It is setting in a kitchen type area and takes water etc. to warm food. I just assumed it should be on a GFCI. Guess I assumed wrong:(

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#214973 - 02/17/15 01:02 PM Re: Food warming table on GFCI circuit [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
I bet that if you put a ground plug adapter on there and hooked your clamp around the grounded pigtail, you would see leakage current. That is really interesting with a scope on a fridge that trips GFCIs. You can visualize the sparking that is going on inside the compressor.
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#214974 - 02/17/15 03:47 PM Re: Food warming table on GFCI circuit [Re: renosteinke]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
ANY steam table is going to be corrupted by bad feed water.

&&&&&&

The FIRST ocean going steam engines -- pretty much through the 19th Century -- used an open cycle -- getting their feed water DIRECTLY from the sea.

They were built in such a way that their boilers would be serviced -- de-scaled -- at virtually every port. (The original transits were between America and Europe.)

This stupidity went on and on. It took years after the Carnot ( pronounced: kar-know ) theoretical (reversable) heat engine cycle discovery in the mid 19th Century for the designers realized that a closed cycle (totally recirculating (the water and steam) engine) was THE way to go.

**********

Which brings us to modern steam 'tables.'

[ BTW, to an engineer a "steam table" is a graph or spread sheet array showing the various heat dynamics of steam vs water vs vapor. They were originally developed by Scotch Wiskey distillers -- to get their 'pots' correctly tuned. ]

ANY steam table that has an open cycle needs make-up water.

If the energy comes from resistive coils -- then the make-up water HAS to be extremely pure -- or the device will fail.

Merely softening the water ( salt, ion-exchange beads ) will prove pretty much useless.

The feed water needs reverse osmosis to get ALL of the minerals out of the stream.

This will prove true -- even if the local area has a reputation for 'soft, pure, water.'

As far as the manufacturer is concerned -- this tick assures plenty of after-market service calls and replacement parts. No need to inform the buyer/ user.
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#214975 - 02/17/15 04:14 PM Re: Food warming table on GFCI circuit [Re: gfretwell]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
The hermetically sealed refrigerant compressors have morphed away from mechanically switched (capacitive start) single phase designs.

Gradually, solid state, time-delay relays switched out the starter coils. This scheme would eliminate 'sparks.' However, the very nature of solid state switching dynamics causes 'harmonic skew' as the hyper-speed of the switching causes AC wave energy to 'kick back.' This tick is the rationale for SNUBBING resistors. The cheesy price pressures of the market must have had the early designs lacking any such 'wave quality' protection. (no snubbers)

Such a wave kick-back would be certain to trip a GFI at the lower thresholds. ( the common GFI on the shelf ) You'd have to install the (expensive, low demand) GFI which is tuned to let this distortion pass by without tripping. ( seven to ten times as insensitive, IIRC )

The LATEST (European) designs have morphed over to VFD. This scheme is largely government mandated -- to save energy. ( The manufacturers induced their European government (Brussels) to compel themselves to do what they wanted to do... bring out a new generation -- at a new standard -- that is not manufactured outside Europe.) (Well, at least for a while)

Like all VFD schemes, the line side current is rectified into a 'tank' of DC -- with a sweet buffer of capacitors... the 'tank.'

Then the DC is chopped into a synthetic THREE phase AC to drive the load side motor. This transformation is now so efficient that the design runs at lower power -- and with a virtually unlimited life. (until it leaks, or the SS drive fries)

This (pricy) scheme makes (economic) sense where juice is very pricy -- or politicized. (European 'Greens' are all about such tech)

One should expect to see this scheme enter the commercial refrigeration market in North America -- and then Congress will follow the Europeans and mandate it.

In some jurisdictions, the government even cross subsidizes their purchase. (the various Poco utilities issue a purchase rebate funded by the general rate paying electrical consumers -- very much in the style of the PV rebate programs we've all learned to love.

Of course, VFDs are notorious for dumping high-harmonics back onto the neutral/ return conductor.

All of which means that one can't really be certain if ones scope is reading actual sparking from a classic mechanical cut-out relay inside the hermetically sealed compressor -- or if it's bad wiring -- or if it's solid state 'recoil energies.'

It'd be nice if these machines were labeled -- and had a diagnostic jack that could be tapped -- just like those in modern automobile production. They are already being controlled by solid state chips. This would increase their manufactured cost by 0.01 % of the retail price.

This is all a part of the "Internet of Things" -- where all electrical power devices will become addressable -- which is already being proto-typed/ demonstrated.





Edited by Tesla (02/17/15 04:19 PM)
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#214976 - 02/17/15 06:34 PM Re: Food warming table on GFCI circuit [Re: sparkync]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5300
Loc: Blue Collar Country
Maybe what we're discussing are different things.

When I think "steam table," I think of a buffet counter with pans set in it. The bottoms of these pans rest in a pool of water that is kept hot - not true steam; just hot water. No circulating system, just a big tub with water and heating elements.

The elements I'm used to seeing are 240v, and are hard-wired to a control unit. The control unit usually plugs into an appropriate receptacle under the table. The supply wires are usually #8 or #6.

This places the circuits beyond what is usually protected by a GFCI.

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#214978 - 02/18/15 12:07 AM Re: Food warming table on GFCI circuit [Re: sparkync]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
I'm glad you cleared that up.

I've seen steam driven cooking kettles used for food -- and explosives. ( TNT is usually melted this way to produce munitions. )

Because of the nature of pressure and heat and the above listed steam table data sheets, one can dial in a remarkable steady heat -- without temperature spikes.

This is why such schemes are exclusively used to melt chocolates.

There is another type of 'steam table' in use: to prep oriental foods prior to freeze wrapping. The various vegetables are steam processed -- at higher temperatures than chocolate -- until 'just so' -- and then flash frozen.

Such food processing steam is typically electrically powered... lending itself to process control, too. Whatever the mechanism, any steam generator that does not have an absolutely pure feed corrodes into junk with amazing speed.

For locomotive buffs, the front face of the old steam locomotives existed entirely as an access point for the anti-corrosion crews. If you inspect them closely, you can see that the entire front can be unbolted, removed.

Thereafter the boys have to ream out any corrosion from the endless boiler tubes. This one process absorbed the bulk of all of the maintenance budgets of the era. Most locos were treated two to four times a month -- or even more in areas of bad water. It was so bad in the American southern desert that the SP hauled in pure water for certain locations. (!)

Sorry, my bad, Reno.
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Tesla

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#214980 - 02/18/15 01:00 AM Re: Food warming table on GFCI circuit [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
Tesla, I was just talking about shorts in the motor windings themselves, not a start switch.
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Greg Fretwell

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#214982 - 02/18/15 07:25 AM Re: Food warming table on GFCI circuit [Re: sparkync]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6786
Loc: Brick, NJ USA
Interesting. From a food warming table, to locomotives and steamships!

Tesla: The extent of your knowledge is amazing!!

Would not a solution be to split the 4 elements into two sets of two.?? 2x120 volt, 20 amp circuits??
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John

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