Blue M Oven

Sorry I can't go much further tonight, but for now:

"1) I would like to know if I need a ground connection."

Yes - emphatically YES.

With the possibility of 480V appearing on the outer casing of the equipment under fault conditions?

YES - CONNECT AN EARTH/GROUND CONDUCTOR TO EXTERIOR METAL PARTS BEFORE ATTEMPTING TO ENERGISE IT!

If in doubt, consult a qualified electrician locally.

I humbly apologize for the wrong use of words!

The oven chassis is grounded.

I meant to ask if I need a neutral wire.

I assume that was a delta connection for the heaters (although one leg is different from the other two, as consumption). Do I still need a neutral if I want to use capacitors for filtering?

The power is brought to the oven distribution panel over three wires (of a strange combination of colors : black, white, green to a junction box and, continuing to the oven, orange, red, and white).

That doesn't sound right at all for three phase wiring in US.

I would advise a very careful examination of the existing system and design as it sounds like it was not wired properly (and who knows what else is wrong). I would also advise getting any drawings and manuals for the existing system FIRST to assist in the design and wiring (especially if you are inexperienced in the field of three phase power, and the equipment is in pieces). Have you tried the heater manufacturer's website for information on the design and wiring of this or a similar heater?

Additionally, do you have access on site to a three phase and neutral supply (ie- a 5 pin three phase power socket)? That's how I normally get my neutral for single phase (Neutral referenced) electronics working with a three phase Delta system.

Perhaps you should be working with an electrician on this one from a practical, safety and legal point of view (hint, hint).

...do you have access on site to a three phase and neutral supply (ie- a 5 pin three phase power socket)? That's how I normally get my neutral for single phase (Neutral referenced) electronics working with a three phase Delta system.

Not having a schematic I was afraid that, if I connect the heaters in a delta connection I might fry them if they were to be connected star. That's why I asked about the neutral. Also, the neutral would have been a reference for the three phase filter capacitors.

But I have the schematic in hand, now, and there are only the L1, L2, and L3 wires coming to the oven.

There is a 480/120 V transformer from which I am going to supply all the controllers, 24v supply and protection circuits. The secondary of this transformer is shown, in the schematic, that it has to be grounded.

For 480VAC incoming power the color code should be Black, Orange, Yellow, and of course green for the ground. You do not need a neutral, Blue M ovens use a control transformer for the 120vac. You should have a safety instrument and a seperate control instrument which are powered by the control circuit. Most of the Blue M's that I have worked on, use a contactor for the heat control, and a contactor for the safety. And most of all, a door switch to shut off the elements, if they are of the exposed type, while the door is open.

Call Blue M for a schmatic. Usually they will give you one, but it may take a week to get it.

Thanks, buddy.

You are exactly on the phase!

The schematic confirms what you have said, no neutral. The only grounding is done on the secondary side of the 480/120 V transformer.

There are, at the final count, only three equal (cold) resistance heater resistors that I will connect in a delta configuration.

As for colors, they are as you have said at the main distribution box. The colors of the wires to the oven must be the artistic vision of the one who pulled the wires (over here, in Houston, there are a lot of illegal...electricians).

I guess that I have to dig a bit more, there are capacitors that form a filter with the 1.5 Henry inductors but I don't know, yet, their value. Probably I will call the manufacturer.

For me, not being familiar with 480V, and with large voltage distribution (please note that any voltage over 12V is large, in my book ) it was a big deal to know if that neutral wire is necessary.

The rest of protection circuits that I am introducing on the vacuum distribution, vacuum pumping or electrical are somewhat simpler, for me.

Allow me to mark GA for your answer.

Indel

Good morning, Indel,

Firstly, congrats on ending the dry spell. I've been through a couple myself and I know they're no fun!

Now to the not-so-good part. Not tellin' you what to do, but y'all might oughta think about contracting with a licensed electrician for this job. There are all kinds of state, local, and federal codes that regulate this type of work and I'd hate to see anyone run afoul of 'em.

Regards, and good luck on the new job!

Logan

Hi logan,

You are right, not funy at all when it is dry. As for the colors of the wires, they are not conform with what rrnut-2 mentioned for three phase 480 V, but they are pertaining to the oven circuit, in a metal conduit. I have told the owner about the colors and he just took note. That after I told him that I would like to see a green (or whatever color) wire for the neutral. He lokked at me and told me that he uses Blue M since '70's and some have and some do not have neutral...

The not so good part is that it is a project that will end next week.

Take care

indel

Yep, confirmed by an engineer who works at Blue M ( I eventually was able to contact them).

Only three wires from the 480V 3 phase distribution.

The transformer that provides 120Vac (from 480Vac), for internal use, has one wire grounded.

There are four heaters, in two ceramic bodies. In one body there are one heater of R cold resistance, and one of R/2. The two R/2 heaters are connected in series to form a heater of R resistance. All three resulting heaters are connected delta.

Now, the most important thing: A delta connection will not produce a third harmonic in the system. The capacitors are kind of filtering for the old system with SCR (back to back). Mark (the engineer) told me that they have removed the capacitors, being too much trouble with component failures. But the 1.5 H inductors stay. I haven't energyzed, yet, the system. I, still have a small problem. The current reaches the maximum in this inductor in some 18 ms (calculated). Has, one of the dragons of the three phase loads, any comments? (I will verify this next week).

Why not contact the manufacturer?