Help >> Boiler Element Wiring?

[olivermr]

Hi Guys

Please can you help? I am rewiring a +/- 300 litre boiler aboard my vessel after determining that 4 out of 9 elements had bad insulation to earth and were tripping the shore power (old boat with old breakers and a higher sensitivity shore breaker). Currently to even the load across the 3 phase supply I have powered the elements in sets of 3, 4 connections to each element. I run 2 sets of 3 permanently and leave 1 set for redundancy. So i currently have one set working and two elements left. My question is how I should temporarily spread the load the two remaining "good" elements across the 3 phase supply.

Thanks for your help
Mark

 

[nimbusgb]

Way beyond the scope of most people here methinks!

A 300 litre calorifier is beyond the dreams of most people here and 3 phase electricity is AFAIK unheard of.

IMO who cares which phases they are on if they are redundant spares

 

[DaveS]

If I understand correctly, you have disconnected the 4 elements with earth faults and wish to re-connect the other 5. You have already connected up 3 in "star" configuration to the 3 phases and neutral, and wish to know how to connect the remaining 2.

I would suggest looking at which phases supply your other major single phase loads and, if you can identify one phase as heaviest loaded, connect your elements to the other two phases. That should give optimum phase balance over the boat as a whole.

With 4 already gone faulty, however, I would expect to see further failures later, so it might be a good idea to get replacements.

 

[mikehibb]

Any chance of make and model number?

There are diferent ways of wiring a three phase heater/boiler.
Some require sets of 3 wired in Y but without the neutral points interconnected between each set.

Need more info on the make and model.

 

[olivermr]

Hi Guys

Thanks for all your responses! Really appreciate it! Ok i will try an anwser each of you seperately for clarity.

DaveS:

My current wiring for the set that is working cant really be classified as star as we do not have a neutral on board just the three lines L1, L2 and L3 and and earth which connects directly to a GFCI breaker on the shore through a four wire cable. I have taken your advice about the phase loading and have through the 3-way Line ammeter on on the main panel been able to determine that I have the least amount of current following in L2 so will connect the elements so that L2 carries the most current i.e. load. I agree that I may have further problems but I have established the the original fault which were leaky bolts connecting the front boiler elent flange that droped water on the elements and through sparking have caused a 100 to 700Mohm path to earth. So willl be removing the bolts and sealing them better this time.

mikehibb:

Unfortunately mike the make and model might be quite in significant as the vessel is almost 42 years old. But as I have explained above there is no neutral on board i.e. calorifier/boiler simply has three Lines L1, L2 and L3 coming from the contactor in the control box. Each element has four screw connections for convience we can say A, B, C, and D where A-C and B-D are the element connections taken that A is at 0 degreees and D is at 270 degrees. I will try upload a couple photos. The elements are 2KW rated for 380V so with 2 sets running I am drawing about 30A.

Thanks again for the help.
Regards
Mark

 

[olivermr]

Photos

View attachment 2815

Hi guys hopefully you can access these. I used Winzip.

 

[philip_stevens]

Hi Guys

Please can you help? I am rewiring a +/- 300 litre boiler aboard my vessel after determining that 4 out of 9 elements had bad insulation to earth and were tripping the shore power (old boat with old breakers and a higher sensitivity shore breaker). Currently to even the load across the 3 phase supply I have powered the elements in sets of 3, 4 connections to each element. I run 2 sets of 3 permanently and leave 1 set for redundancy. So i currently have one set working and two elements left. My question is how I should temporarily spread the load the two remaining "good" elements across the 3 phase supply.

Thanks for your help
Mark

It sounds as though your 380v elements are connected in Delta configuration.

The 9 elements were connected as 3 banks of 4-in-parallel, balancing the load on the 3-phase supply.

You need to balance the load across each phase - whether you have 1,2,3 or 4 elements in parallel will make no difference to the balance, only the speed of heating and current load, as long as there are the same number of elements across each phase.

From what you say, it also sounds as though you can switch the sets, to have low and high heating. It is possible that these can be wired to a multi-contact high current rotary switch to give low, medium and high - as in 3-phase galley ranges.

If you have any circuit diagrams, send me a PM with your email address, and I will reply with my email address for you to send me a diagram.

 

[mikehibb]

We had a look at the pictures today at work.

Firstly it looks like each "element" (set of 4 terminals) is two elements (with both ends of each element available for connecting to)

Looking at the group of three in the picture we redrew it as 3 groups of 2 elements, then joined up the dots as per the wiring, to come up with what appears to be a delta wiring with two elements in parallel on each side of the triangle.

Assuming that the larger cables are the L1 L2 and L3 connections to the contactor.

Do not suppose that you have a picture of a bare element removed from the heater.

We were also wondering the country of origin of this heater, is it USA?

Great little project this, I have a trainee electrical engineer at work (who will eventuallu have my job) who is also benefitting from this.

Any additional info much appreciated.

(ps we recently reconfigured a 3 phase delta 250KW heater to Y connection in banks off parallel Ys without neutral, the star points in this configuration must not be interconnected)

Mike

 

[olivermr]

Hizit Guys!!

Sorry for the late reply but going through a couple crew issues onboard! Anyway no problems now so we can get back to it!

Ok so after doing exactly the same thing as what you have done Mike I have realised that the system is wired as three parrallel Delta banks/sets with 3 elements in each (2 arms per element 6 arms in total per set) of which as you say 2 arms are in parallel per inter phase connection.

So progress.......well after my first email my chief eng wanted something done so I went ahead and connected the remaining two elements (4 arms) up. Obviously because of there being 4 arms I could not balance the load on the phases so one phase took the extra element arm. The result was a difference in phase current of approximately 3 amps. Two phases carried 7.8amps and one carried approx 4.8 amps. The problem was that on reconnection and bringing the boiler back to temperature one of the elements failed due to the insulation problem we have been having. Before reconnection the element registered perfect insulation. After reconnection running and disconnection from the system the element started to display intermittent insulation oscillating between "OL" and 750Mohm using a digital insulation meter. I can only think we need to replace all the elements with properly insulated units! Anyway that star (Y) rewiring sounds interesting? Does this alter the performance of the boiler at all?

Philip thanks for reply. I unfortunately do not have a circuit diagram other than one I sketched by myself after studying the system some time back. The unit does not have a 3 phase rotary switch and it is merely on or off depending upon the temperature sensor which is set at around 45deg. Thanks for confirming my belief that there should be an even amount of elements across the phases. Would a mistake in my wiring effect the power factor efficiency of the 3 phase system? You are exaclty right that if I have 9 elements when operating 6, 4 element arms shall be in parallel across the phases.

Thanks guys! Really given me insight!

Regards
Mark

 

[olivermr]

Oh forgot to tell you Mike the vessel is dutch and was refitted in the US so yea it probably is an american system? Why do you ask? Or how do you know that?