Help to Identify This Schematic Symbol

Looks Chinese....maybe alien...

Are you referring to the fuse symbol?

http://en.wikipedia.org/wiki/Fuse_%28electrical%29

For all we can tell, this may be a symbol for showing in a single-line diagram a fuse feeding a transformer primary.

Could be a fuse for indicator light...

HDR don't have intrests in fishing by any chance? It looks like the symbol for a Lure!

According to my ARRL handbook, 1961, that oblong thing is a U.S.A. fuse symbol. You say it is "a CT neutral bond for incoming power" which is not crystal clear.

Bond to what? Ground?

Is it a bond conductor from neutral to ground with a CT around it?

Or is the bond from the CT secondary to neutral or ground, via the "fuse".

I have always regarded it as customary to ground CT secondary circuits, to stop them getting dangerous voltage via their capacitance or insulation failure.

This is often via a removable link, to allow insulation testing. Physically, this has been done with a solid link in place of a fuse, in a fuse carrier - but the symbol is different to a fuse and the circuit ident is LK.. not FS.. to avoid error (holders also paint marked white), because fitting a fuse in an earth connection is bad practice [practically illegal].

I recognize a portion of the symbol to look like the symbol for a fuse. The drawing states "...Connect neutral bus to ground bus at one place only thru (sic) CT for ground fault protection."

For all apparent intentions, this is the service bond for the facility. That is partly why I don't understand why a fuse would appear in that function...that would be illegal and just plain silly in my mind. No value appears for it (the "fuse") any where in the drawing set.

Looks like a kelp anchor to me.

Tis a cod jigger, b'y.

Or maybe it's a symbol for 'where to put your parasitic bug', DoE.

You are correct that the first symbol is a fused PT, but only showing the primary side. In a fairly high level 1-line drawing, the details of what are on the secondary side may not be shown.

The second is a CT with relay(s) that require a current input. Usually the "R" is replaced by the ANSI device number representing the type of relay (e.g., 50 for instantaneous overcurrent, 51 for time overcurrent, etc.). In the case of the OP's example, it's from a generic set of symbol examples, so they jsut used R.

The third is a PT with relay, similar to the way the CT is done.

These examples are pretty common ways of drawing the items in electrical power 1-line ddiagrams.

Raef...thanks

My symbol that needs defining is the first one. The other two symbols were from the only reference which appeared similar. My drawing indicates (infers) this as the service bond for the facility. This does not makes sense to me. Nowhere else in the drawing set is a bond indicated. Short of powering down the facility I have no way to verify the ground and/or CT arrangement indicated.

As to your NEVER statement...that only adds to the mystery. The callout for that connection states "Connect neutral bus to ground bus at one place ony thru (sic) CT for ground fault protection."

The symbol index/legend does not include this symbol...quite frustrating.

It appears from your explanation that someone chose the wrong symbol to use at your neutral to ground bonding point. It should just have been a straight line with a ground symbol at the end. It would not have a fuse in it. It would have a CT with relay similar to your second symbol, to detect current on the neutral above some specified limit for phase unbalance or ground fault detection.

Your note suggests the correct physical construction, that the neutral to ground connection be made "through" (the primary window of) a CT, the secondary of which is connected to a GF relay. They just drew it wrong.

Unfortunately for me this is a single line diagram which does not normally indicate individual phase/neutral/ground wires. This symbol appears on each (3) individual bus for the switchgear, however other drawings indicate the wye/ground connection point (in graphic format, not schematic). Nowhere on the drawings is the neutral/ground connection actually indicated.

Having read your description, cuba pete, and the various comments, I think this will only be solved by examining the wiring diagrams/circuit diagrams or tracing the actual wiring physically/by a cabling diagram.

Probably one of those cases where a single line was drawn at an early stage, but no-one ever went back and made sure it showed "as-built".

For example, first thought was neutral grounding via a PT or power transformer with secondary resistor (hence the fuse) but it ended solidly grounded with a ground fault CT and current relay. Then the description was changed, but not the symbols (someone marked-up the drawing with words, without changing the symbol, and the draughtsman just changed what was marked).

Thanks to you and to JRaef for the links.

Where did I miss out? I've been working in electronics for over 60 years, and I had never heard of nor seen a 'single line diagram'. Are they used for power distribution and control?

Electronics and power distribution are very closely related fields, but each has it's own particular symbol set.

For instance, I have seen normally open contacts interpreted as a capacitor by some techs, and electricians that would never use a black wire for ground, or a white wire for signal.

I have had the good fortune to work in both fields for over 50 years,as well as pneumatics, hydraulics, process controls(PID's) but they come up with new and strange(to me) symbols every day.

NPN,PNP, UJT, SCS, SCR, EMODE JFet, DMode JFET,TRIAC,Zener, just to name a few would be totally foreign to electricians.

What we recognize often dates us.

What modern tech would recognize the symbol for the various vacuum tubes,

or a selenium rectifier?

I am sure there are many I would not recognize also..

Yes, one-line diagrams are used in power distribution, not "bit twiddling". As a power engineer i had to learn all about electronic symbols, yet one can get a complete EE degree focused on electronics now and never come across this. It's not as uncommon as you might think.

Yes, power distribution for facilities...hotel and technical power...is usually referred to as a "one line" or "single line" diagram. All of my time has been in the US military, so maybe that is peculiar to us.

The problem is, there is no "official" single line diagram symbol that is designated for a Zero Sequence CT for a GF relay setup. So people essentially have to choose their own way of depicting it. To top it off, single line diagrams almost never show ground or neutral connections, they are intended to depict power distribution. So they will show "one line" for power and then describe it as 3 wire or 4 wire, with or without ground, but not necessarilly depict them. If so, then depicting a Zero Sequence CT in which the Neutral must pass through it along with all 3 power lines becomes a "challenging" choice. Then for clarity they (should) also show an actual wiring diagram that will specifically depict how they expect it to be connected.

This person chose poorly.

Typically on the One Line, I just show a standard CT symbol and put a notation next to it that says ZSCT, then show it connected to a rectangle that says "GFP" for Ground Fault Protection (or GFR for "Relay") with a connection to a circuit breaker Shunt Trip symbol (if it has such).

Something like this: