Electric code or UL question, SPST relay on pump

Ultimately yes, it'll have to go through UL anyhow. I was just wondering if anyone knew so I could pick an enclosure. It's a really tight fit in there and if we need DPST it means not just a bigger box but also other power connectors and stuff because else it's not going to fit.

AFAIU they mean just the relay innards and the pump power still comes from the mains line.

That won't be helped with a DPST relay because this kind of fault can and does usually happen while the motor is running.

It'll be single-fault safe with SPST and DPST. I just don't know if SPST is legit (mainly for the US). In the end it's only legit if the test guys say so but they typically won't voice an opinion until the whole enchilada along with a big check gets there.

Certainly a nice option but would require a laid out board. The client wants it all to be pieced together from COTS parts. Ideally without requiring much beyond pliers, screwdriver and a crimp tool.

Here most plugs are only polarized if they have a ground pin, which most don't since they won't fit in the large number of sockets without ground and most stuff is delivered with a schuko plug which doesn't connect ground in a Danish socket.

But all homes are required to have a GFI

-Lasse

that fault & the relay are separate issues. The fault scenario you have to consider to meet UK regs. You're not allowed to have 240 on the case while the fuse melts.

SPST is fine for UK, which uses all polarised plugs & wiring. I can't help with other countries.

NT

The key is if the water is connected to ground (metallic plumbing). Complete circuit, ya know.

You'll have to go directly to UL but building codes do not want DP switches in 120V circuits. They want the neutral connection unbroken. However, codes only apply to buildings, not equipment, and there are often differences.

The difference is that you have a balanced power system, so you have to switch both "hots". 120V circuits in the US split-phase system are unbalanced and only the hot is switched. You really don't want to break the neutral/return.

neutral ~= earth, three 230V phases

Uniform (and your local/state) Building Codes dictate this for buildings. The same arguments hold for equipment but UL is the (or more precisely "an") authority.

Yes, that sort of nonsense was common here fifty years ago, too. Remember the "All American Seven"? Since then, we have polarized plugs and GFCIs where grounded plugs aren't economically feasible.

Wow, you're way higher tech than the rest of us--all of ours were "all-American fives". ;)

Cheers

Phil Hobbs

I guess I don't remember all that well. I guess I'll just claim that it was before my time. ;-)

I've always wondered about the multiple barrier concept. If there are two barriers, each one sufficient for safety, but neither detectable, a product could have one fail which then leaves you with just one which means it no longer meets the requirements. If the failures can happen without any indication, one of the barriers could fail before it even reaches the consumer and no one would know.

There are at least three dozens of countries using the unpolarized Schuko (Type F) socket and plug.

In addition to this, the Europlug intended for small (2.5 A) double insulated equipment can be inserted either way also to some other sockets with asymmetrical PE pin,i.e polarized sockets.

So if you intend to sell on the international marked, either have a double pole switch or have double insulation.

In Europe, tube TV sets were AC/DC type. A half wave rectifier provided the 170-200 V anode voltage, while P-series (300 mA) heaters were in series across the mains voltage. With unpolarized plugs, the metal chassis was ether at the Neutral potential or the full 220 ac Live.

When servicing a TV set, the first thing was to check the mains plug polarity so that Neutral potential was on the metallic chassis. Later on, an isolation transformer was required for each device in a TV repair shop.

With the 50 % chance having the Live in the chassis also meant that providing an external connection would be quite expensive. Usually only a RF-transformer isolated antenna connector and possibly an external speaker connection from the audio output transformer were provided.

No we don't. Quite the oposite, we have a lot of PME systems where the neutral is grounded at multiple points.

NT

sometimes it does. That's why there are 2.

not so

Rare. More common is one of the barriers is missing.

NT

All the ones I've seen used capacitor isolation for the aerial. A plastic disc is cheaper.

NT

A class II appliance requires no safety earth but relies instead on two, *i ndepandant* layers of insulation to protect the user.

The first is merely "functional" insulation, which any appliance needs in o rder to work. The second layer ( called reinforced insulation ) protects th e user in case of failure of the first layer.

Many Class II appliances have no exposed metal parts, so are inherently ver y safe. The ones that do have exposed metalwork take special precautions so live parts and exposed metalwork can never come into contact - unless the item has suffered obvious damage.

Supply connectors, switches and transformers used in class II appliances mu st be designed and rated for such use - where their failure could render ex posed metalwork live. The design rules and test procedures for class II rat ed supply transformers are elaborate, involving fire proof insulation and t he use of regular plus thermal fuses so no possible overload condition resu lts in a hazard to the user.

But nothing is perfect and end users must take basic precautions - a water soaked class II power tool must not be operated nor a class II hair dryer d ropped into an occupied bath tub.

.... Phil