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Electrical protection for multiple devices vs per device protection

Electrical protection for multiple devices vs per device protection


  #1  
Old 03-18-15, 06:05 AM
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Electrical protection for multiple devices vs per device protection

So I woke up the day before yesterday to the wonderful smell of sewer. Waste water pump had given up the ghost.Guy who sold me a new one said that proper electrical protection will do wonders to extend the life of a pump.

I have a couple pumps all connected to one subpanel, is there any reason not to use an appropriately sized protector for the subpanel rather than one for each device.
 
  #2  
Old 03-18-15, 06:42 AM
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Which kind of protection was he talking about? With pump motors it could be over-current protection (breaker or fuse), GFCI / RCD / EFCD (electric shock protection), thermal overload protection, dry well / low or high pressure / protection, etc...

I see your location is non-US, where more specifically?
 
  #3  
Old 03-18-15, 07:00 AM
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He said high voltage or low voltage specifically but to talk to an electrician .

I'm in Argentina, 220v.

The subpanel is on the opposite side of the wall from another panel.

That panel has a GFCI on it, and the connection to the pump sub panel is protected by a 16a 2 pole breaker, the sub panel consists of another 3 16a 2p breakers. 1 for the newly purchased sewage pump rated at 1.5 hp. 1 for the 3/4hp rainwater pump (recently replaced as well) and 1 for 2 fresh water pumps. The sump pumps have built in floats and are completely automatic (until they fail spectacularly that is). The fresh water pumps have a low voltage control circuit connected to another water tank on the roof, each of them is rated at 1/2hp.

Brownouts are not all that uncommon here and we have a moron for a neighbor who blew up the service connection last month and the power was on off up and down for a couple days which I'm convinced could have something to do with the failure of the pump, I'm adding this info because while the explosion and the screwdriver missile seems to have cowed him for the moment, there is no guarantee he's not going to do something really stupid again some time soon.

These pumps cost around $500, replacing them has lost its novelty.

Edit: Now that I think of it, 16amp circuit breakers are really oversized for those pumps.

Edit 2: I had imagined something like this between the breaker from the main panel to the subpanel.

http://www.amazon.com/Monitoring-10-...ription-iframe

Edit 3: I'm going to call my Electrician for this, I just wanted to get a grasp on the situation so I can understand what he tells me.
 

Last edited by Esand1; 03-18-15 at 07:52 AM.
  #4  
Old 03-18-15, 07:56 AM
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Ok it sounds like you are pretty well set up. You didn't mention the size of wire to the subpanel, but as long as that is reasonable I don't see a problem with the wiring in the panels or running to the pumps. Are any of them a great distance from the panel, more than about 100 feet / 30 meters? In the US the smallest breaker you can find in standard stores is 15A, so I'm assuming the 16A is pretty similar in Argentina. That is a reasonable size breaker for the pump motors you listed. If you want to add some additional protection you could install in-line slow blow or time delay fuses on the pumps closer to the actual amperage. This will have a better chance of blowing the fuse during a brownout rather than burn out the motor, and fuses are comparatively very cheap. The industrial control devices you linked could be part of a gold-plated solution but that may end up being very expensive compared to fuses.

On motors high voltage isn't really a problem unless it is really high. Low voltage can be a big problem because it causes current (amps) to increase which adds heat to the motor, lubricants break down, bearings fail, etc.
 
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Old 03-18-15, 10:01 AM
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The sub panel is about <10 feet from the pumps

It could be that 16amps was just the smallest fuse, I just checked and other than a couple 25a breakers everything else 16.

The reason I said it seemed oversized is at least for the smaller pump. 3/4 HP = 550w / 220v = 2.5A x 1.75 for being a motor load = 4.375.

Edit, the industrial control device I linked would run me about 200 dollars for a top brand and 90 for a mid range brand, and 40 dollars for an uncertified Chinese house fire starter.
 

Last edited by Esand1; 03-18-15 at 10:47 AM.
  #6  
Old 03-20-15, 06:45 AM
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Motors usually do just fine with larger breakers than you would think because the motor has a built-in thermal protector so the breaker is really only protecting against a short circuit. Not all motors have a built-in protector so you can either add one as a separate fuse or built in to the starter (which small motors don't have). If you put a 5A or 6A fuse on that motor it will be quite well protected.
 
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Old 03-20-15, 07:19 AM
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Every light, appliance, etc. has a "maximum circuit amperes rating" as well as a "recommended circuit amperes rating." If the max. circuit rating is not published, use the recommended circuit rating as the max.

Sometimes the max. circuit rating is implied, such as from the power plug. Ordinary lights and small appliances with 15 amp plugs in the U.S. have a max. circuit rating of 20 amps.

Because of the max circuit rating, you could not connect, say, two 15 amp pumps to one 30 amp circuit (if each had a 20 amp max. circuit rating).

No light or appliance will draw more current simply because it was connected to a higher ampere rated (or protected) circuit. The max. circuit rating provides some protection from excessive currents in the event of some failure within the equipment.

Brownouts often cause motorized appliances to draw more current and overheat. Usually the max. circuit rating or actual circuit rating is not low enough to prevent this kind of failure. Motors may be equipped with thermal protectors for low voltage overload or other overload. Prolonged overvoltage requires a voltage regulator, or an appliance designed to run using that higher voltage. Brief overvoltage spikes are the subject of surge protectors.
 
 

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