230v DC worries

[TommyBoy]

Hi all, this is my first post on electriciansforums.

I'd like to know if anyone has any experience with temporary lighting systems using rectified mains voltage.

I have started a new job installing lighting for a company that make festive decorations for events and one of the products used is a glorified set of fairy lights which requires an in-line rectifier, not something I have come across before. My experience with DC voltage is limited to working around UPS systems in offices and something I'd usually steer clear of due to the increased danger at these voltages.

Am I right to be weary of this?

Thanks

 

[amlu]

getting shocked by DC is much more dangerous than AC...
and rectified mains voltage will get you something like 290V DC.
do not do it...

 

[Octopus]

How about a 110v tranny and a set of off the shelf lights??

 

[TommyBoy]

getting shocked by DC is much more dangerous than AC...
and rectified mains voltage will get you something like 290V DC.
do not do it...

Thanks, this is what I thought but needed a little reassurance. There's a great deal of pressure from the designers to get things looking 'just so', seemingly with no understanding of the dangers of using some of these products. Looks like I should stand my ground and push for ELV products. Being used outside in the public domain just rings too many alarm bells!

 

[TommyBoy]

How about a 110v tranny and a set of off the shelf lights??

The problem I'm up against is the equipment used is chosen to fulfil the design spec, if they find something that does the job they need they use it. They've bought a lot of these and will probably use them on this project, I'll just have to put them off using them in the future.

 

[Knobhead]

If they already market the product what’s the problem?

 

[Knobhead]

Just to add, DC doesn’t hurt any more than AC and it doesn’t cause defibrillation

 

[davesparks]

This sounds like another one of those products which has been created for the sole purpose of irritating the hell out of those of us who work as production electricians on events. They turn up a few hours before the event goes live and expect me to pull a randomly sized supply out of my arse in the middle of a field.
For the love of all that is holy why can't it just use a bog standard 240V supply on a 16A plug ?

 

[Marvo]

Usually any system that requires a weird voltage or rectified supply would come with a panel that contains appropriate controls, safety devices and the transformers and rectifier. The sparky would just provide a standard 230v or 380v 3-phase supply to that box. If they're designing the lighting system then whoever they are they should be designing the rest of the gear that goes with it. They know the specs and requirements of the lighting so they're the only ones in a position to do this safely and accommodate any manufacturers requirements as well.

 

[davesparks]

That is the theory yes, and it generally works that way in installation work. But temporary event work is a whole different ball game, you will get people arrive on the morning of the event expecting there to be power available in the middle of nowhere, of a random size and connector which is completely inappropriate and wonder why you can't just pull this out if your arse on the spot. After 3/4 days of building the event according to the specs submitted beforehand where they told is that they did not require power.

 

[Knobhead]

Beats me why people are so nervous of DC.

Everything at an event is designed to annoy you Dave.

 

[davesparks]

Everything at an event is designed to annoy you Dave.

I'm glad it's not just me who thinks this!

 

[Marvo]

That is the theory yes, and it generally works that way in installation work. But temporary event work is a whole different ball game, you will get people arrive on the morning of the event expecting there to be power available in the middle of nowhere, of a random size and connector which is completely inappropriate and wonder why you can't just pull this out if your arse on the spot. After 3/4 days of building the event according to the specs submitted beforehand where they told is that they did not require power.

Agreed to a point about connector sizes and compatibility of sockets etc but I'd draw the line with a rectified DC system that may require special rectifiers, and OCPD's / RCD's etc. I'd hazard a guess the reason they're rectifying the AC supply is because they're stringing hundreds of solid-state lamps together on the circuit and they're trying to keep the cable sizes sensible by having dozens of them in series. If that's the case they'll probably need filters and smoothing circuits as well.

 

[TommyBoy]

Agreed to a point about connector sizes and compatibility of sockets etc but I'd draw the line with a rectified DC system that may require special rectifiers, and OCPD's / RCD's etc. I'd hazard a guess the reason they're rectifying the AC supply is because they're stringing hundreds of solid-state lamps together on the circuit and they're trying to keep the cable sizes sensible by having dozens of them in series. If that's the case they'll probably need filters and smoothing circuits as well.

This is very much the case, Cable sizes have to be as small as possible for aesthetics. Each decoration has a lot of individual products on, at least six or seven pre-made strings of lights that require a rectified DC voltage plus one or two that require 230v AC!! One area will have three to five of these decorations so I'm having to run AC to each and splitting the load locally with the rectifiers. Although the load is very small, I worry that with the amount of products in use with so many connections the likelihood of something going wrong is increased. Especially if you were to see some of the idiots putting them together, throw some English weather into the mix and it just spells disaster to me.

 

[Marvo]

I think you're playing a dangerous game. If they're supplying the lights and making up the strings I'd insist that they also at least specify appropriate drivers, that way your liability will be limited to the supply itself and installation labour only. If not I guarantee you that when something goes faulty you'll be the one who's expected to carry the warranties and fix it for free because you're the one with the electrical qualification. If you do want to take the risk and specify/supply the rectifiers etc I'd submit your proposed design in advance and get it signed off by the lighting designers and get it in writing that you're warranty liabilities are limited regarding compatibility issues etc.