Instantaneuos Water Heaters

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michaell

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It has been an ongoing confusion as to what type of diconnecting means you should have for instant hot (tankless water heaters). Does anyone know what the proper way to go about figuring out how to connect these water heaters. Some say, "no disconnect", others say "cord and plug" and others say "disconnect switch only". I have been advised to seard NEC code section 422.31. From what I understand this section refers to "appliances". Is a water heater considered and "appliance". I work in a Mechanical/Electrical/Plumbing Engineering firm and all of our catalogs indicate a hard wired connection with no indication of providing a disconnecting means. Another issue is Architects "REALLY" don't like disconnects under the sinks around these water heaters, because the disconnects are bigger than the water heater itself. Does anyone have any insight on this matter so that we can put it to rest?!

Thanks
 
Re: Instantaneuos Water Heaters

IMO it is an appliance the same as a 52 gallon WH in the utility room. I am wondering why you would think they do not need a means of disconnecting power? As far as the size of the disconnecting means is concerned, a circuit breaker of the appropriate size is not very large and you get the added benefit of overcurrent protection at the WH.

Most of these have a large current draw that hits as soon as the water is turned on and stops as soon as it is turned off. They are fairly high wattage and will cause voltage flicker in the neighborhood. If we find them through a voltage complaint, we will change the rate to a commercial rate and install a transformer just for that customer. It will not take a long time for us to get a return on our investment and the neighbors are taken care of by correcting their flicker. The only one left with flicker is the customer who installed the instant water heater. :D
 
Re: Instantaneuos Water Heaters

Some of these are rated at 48 amps, so a cord and plug connection might also be larger than the unit itself. I would consider them an appliance (see the definition in article 100). 422.31 allows the branch circuit breaker to be the disconnect if it is within sight, or to has the capability to be permenantly locked.

A handle lock or padlock attachment can be purchased for most common breakers (Square D QO types, for example). I would assume this would meet the requirements.

Steve
 
Re: Instantaneuos Water Heaters

Charlie:

Please don't take this personal, but it sounds like the POCO doesn't provide a large enough transformer (or wire) to start with if a 50A load causes lights to flicker. Then the POCO blames the customer's appliance because they undersized the transformer to start with.

we will change the rate to a commercial rate
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If the POCO told me I had to pay a higher rate for my power because they didn't like my hot water heater, I wouldn't be very happy.

P.S. Wouldn't a commercial rate be cheaper?

Steve
 
Re: Instantaneuos Water Heaters

. . . issue is Architects "REALLY" don't like . . .
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IMHO you can go nuts with that statement. I have yet to meet an architect who will give you the room that is really needed to install electrical equipment and to allow for any future expansion. Most electrical rooms have the bare minimum permitted to allow the installation of the equipment needed . . . and sometimes the AHJ is backed into a corner to allow the last of the electrical equipment without the proper clearances. It seems like the bigger the building, the more important the architect/engineer/general/owner/etc. who know people to get the screws turned on the inspector.

In case you haven't noticed, I like inspectors. They are generally under paid and overworked. They are required to do more inspections than is possible to do in the time allotted. On top of all that, when is the last time anyone has thanked an inspector for writing up a red tag?

Sorry, I just had to vent. If this offends anyone, send me a PM and I will remove this post.
 
Re: Instantaneuos Water Heaters

Steve, where this causes problems is in the older areas of town where most homes are gas heat and some are not air conditioned. Our secondaries are longer and the transformers are smaller. Someone has purchased one of these grand old homes and are remodeling. They add a host of modern appliances but keep most of the equipment gas (that is what is prevalent in this area). The A/C and instant W/H is all that is added and is no real problem for the most part except the W/H is used a lot and the constant flicker drives everyone nuts.

Our residential rates are among the lowest in the nation but our commercial rates are considerably higher.
 
Re: Instantaneuos Water Heaters

They do cause the poco major problems in old hoods.The one i installed was a 3 stage with total near 24 KW (OUCH )We ran 3 circuits with lockouts on breakers,and the inspector was happy with this.Do to additional remodeling we had to back one of them off.The customer in this case was sold on this idea by the arc.This cost far more than a standard 40 gal 4500 watt and the customer was very unhappy with the flickering,but did admitt they had plenty of hot water.Had they known of this shortfall of flickering they would rather have had a standard heater.
As to disc.why would you treat this any differant than a standard water heater? Direct wire for that is very common.
 
Re: Instantaneuos Water Heaters

Okay! Jim is the first person so far that has indicated that a disconnect is not needed. As for my application, it will be in a commercial buidling, so I don't have "residential issues". The real issue is that I have an 8KW/208v, 1 phase instantaneous water heater and I have everyone telling me water heaters "are" appliances and they "should" have a means of disconnect within sight of the appliance. At 8kw I estimate that I need at least a 50 amp breaker. Now I have three options. A NEMA 6-50P and 6-50R, plug and receptacle or a 60 amp disconnect, fused at 50 amps or no disconnect at all. Which do I need to use?! That is the real question. Can anyone help clear this issue up?!

Oh and yeah, Charlie's right Architects don't like to give room for anything!(Especially Electrical!) :roll:
 
Re: Instantaneuos Water Heaters

You're right Steve66 did clear it up? Apparantley Monday is taking its toll on me and I didn't quite understand at first! But to further clear things up I just found in NEC Section 422.31 (B) in indicates that permantly connect appliances rated more that 300 volt-amps or 1/8hp the branch-circuit breaker shall be permitted as disconnecting means as long as the the breaker can be locked in the open position!
From now on, I'll take this approach, unless I hear differently! Thanks for the help guys! :)
 
Re: Instantaneuos Water Heaters

Quote by Michaell
Okay! Jim is the first person so far that has indicated that a disconnect is not needed
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He didn't say a disconnect was not needed, only that the heater could be hard wired. If it is then what Steve said about the breaker lock would apply.
 
Re: Instantaneuos Water Heaters

Charlie,
Do your rate tariffs say that large loads like the instant water heaters are not permitted on residential services? If so is that unique to your company or is it commonplace?
Don
 
Re: Instantaneuos Water Heaters

Don you beat me to it. As I'm too in Indiana (way up north :p ) But I would have a problem with this too If I had a tankless WH installed (I do but it is gas fired) That was designed for residental use and since in the long run it would use less energy How could I be charged a higher rate. I know our POCO will charge me more if I go over 750kwh a month and I once caught them trying to charge me this when the bill was for 42 days. but I would be up set as if I had a 200 amp service and since I'm not over loading it and the POCO did agree to hook it up, then how could they charge a commercial rate if this service is drawing enough to dim lights but not enough to over load the mains? Are what we saying that we cant use our approved service to it's full potential if the POCO didn't bother to upgrade the lines/transformers at the street? Here if the street lines are not big enough to handle the new load they up grade them. what would be the purpose of having a 200amp service if you cant use it? I know - 20% ok 180 amp's.
 
Re: Instantaneuos Water Heaters

The problem is not the load, the problem is the large load that is activated every time someone hits the hot water. This causes constant flicker for the whole neighborhood until we fix the problem. We have to invest a significant amount of money to fix a problem that benefits only one family. Why should our rate payers pay for something that a single family caused?

We would have no problem with any size of normal load. We do have problems with frequent, large, cyclic loads. :) :D
 
Re: Instantaneuos Water Heaters

Charlie,
We would have no problem with any size of normal load. We do have problems with frequent, large, cyclic loads.
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I understand the problem that is caused, but do the residential rate tariffs on file with the state utility commission spell this out?
Don
 
Re: Instantaneuos Water Heaters

Don, I am sorry, you just went over my head. I just know that we have done it in the past when these W/Hs are causing problems. If they do not, we do nothing about them. I believe we do have something that covers this situation but I do not know what it is. Our rate department is always involved whenever a change like this is made. :D
 
Re: Instantaneuos Water Heaters

I was just visualizing the lights dimming everytime someone turns on the faucett :D
Sound like something out of a bad movie! :D

Michaell: I think were both on the same track. Provide an accessory to attach a lock on the branch breaker in the panelboard, and you should be OK.

One other item: These heaters have always amazed me. I can't understand how they can heat the water from 40 deg to 120 deg when the water is flowing so fast. Does anyone know how they can heat the water so fast?

Steve
 
Re: Instantaneuos Water Heaters

Steve, First off we don't need 120 degrees.Anything over 105 is to hot for a shower.Keep in mind the number of gallon per minute flow is small even in a shower.They do work,the problem is they could easily cycle on and off while using them.Now if this is just one 8kw under a sink i dought the impact would be as severe as a 24 kw in a residential hood.And if your neighbor shares that transformer they will blink with you.
 
Re: Instantaneuos Water Heaters

422.31 b makes it very clear that the breaker with lockout is acceptable as the disconnect.Nothing wrong in going over this requirement,but should do fine for most normal installations.
 
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