Frequently Asked Questions
1. What are the advantages of Mercury relays over Solid State Relays in A.C. Resistive heating application?
Mercury Relays have a Longer trouble free life, cost effective, they have a greater immunity to voltage spikes, lower voltage drops and less heat generated by the units then Solid State Relays.
2. What is the difference between Resistive and General Purpose?
Resistive has a Power Factor of one and usually used in A.C. resistive heating.
General Purpose is a UL designation for loads with a Power Factor of 0.7 or higher.
3. What is the average life of a relay?
At full contact ratings, the relays tend to last several million operations. Running at lower voltages and currents can add greatly to the life expectancy.
4. What is a Liquid Level Control?
The most common liquid level control is the sump pump float. Our floats can be used to control the levels of many other fluids too. The sump pump float is designated a normally open or pump down. We also make normally closed or pump up floats to control the addition of liquid to keep and tank from going empty.
5. Normally Open (Pump Down) VS. Normally Closed (Pump Up)
Deciding whether your float switch needs to be normally open or normally closed for pump control can be a little confusing. So we would like to clear things up.
When we say normally open or normally closed, we are referring to an electrical circuit. An open circuit is incomplete, meaning that the electric current is unable to complete the loop due to a gap. A closed circuit is complete with no gaps, enabling the current to travel through the whole loop.
With level switches, these circuits are opened and closed by the float either moving up or down based on the rising or falling level of the liquid. Deciding whether or not you want the circuit to be closed or opened when the float is either up or down can be tricky.
The most effective way to decide is to determine what the switch should do when the float is at rest. When we say at rest, we mean that the float is not suspended in the liquid. We often see confusion with the term normal as others have misinterpreted it as a float suspended. Remember, normal, in terms of switches, refers to a float at rest.
So, if you want the switch to be energized, or on, when the float is at rest, then you will need the switch to be normally closed. If you want the switch to be de-energized, or off, when the float is at rest, then you will need the switch to be normally open.
Also, it may be helpful to know that normally open switches are typically used for pumps that empty a tank, while normally closed switches are typically used for pumps that fill a tank.
Let us know if you need help deciding whether you need normally open or normally closed switches and we will be glad to help.
6. Where is MDI located?
We are located on US 12 East in Edwardsburg, Michigan about a mile from Lunkers (now since closed down) and not to far from South Bend, Indiana and the Notre Dame Fighting Irish (about 35-40 minutes North East).
For GPS Coordinates: 41.79832, -86.05040
7. Can Mercury Relays Be Shipped to All 50 States? (IMERC States)
Due to mercury-added products being banned or phased out in some states, MDI cannot ship Mercury added products ( Relays, Switches and Floats) to the following IMERC states:
Connecticut (CT), Minnesota (MN), Maine (ME), Massachusetts (MA), New Hampshire (NH), New York (NY), Rhode Island (RI), or Vermont (VT)
These states belong to the Interstate Mercury Education and Reduction Clearinghouse (IMERC) group, which have these restrictions.
Exemptions are currently being applied for in cases where Mercury Relays and Switches are being used to replace relays and switches in equipment originally manufactured with Mercury Relays and Switches. But, currently, MDI cannot ship into these states.
8. Can I order directly from MDI, to another country?
Yes you can just call or use one of our online contact forms and let us know you want to order directly from us. We accept Visa and MasterCard. You may also find that we have a stocking distributor in your area.
Our online store is limited to USA, Canada and Mexico.
9. How should I dispose of my old Mercury Relays and Mercury Floats?
10. Where should I send old relay full of Mercury?
Send them at any one of the following locations:
Onyx Superior Special Services, Inc.
1275 Mineral Springs Drive
Port Washington, WI 53074
Phone: (800) 556-5267
Bethlehem Apparatus Co., Inc.
890 Front Street, P.O. Box Y
Hellertown, PA 18055
Phone: (215) 838-7034
Fax: (215) 838-6333
25028 US 12 East
Edwardsburg, MI 49112
Phone: (269) 663-8574
Fax: (269) 663-2924
For all return goods:
Relays, Switches, Timers, and Floats
Please download and send this form with the goods.
MDI Return Form
Mercury Relay Disposal
MDI Inc. will take back ONLY MDI relays and there will be a $10.00 per pole charge.
To return spent relays YOU MUST:
- You must call us for an RMA#
- Ship them "Prepaid"
- Mark the box "For Disposal"
- All returns MUST be placed in a Tightly Sealed Plastic Container
It is critical that ALL relays be returned in a tightly sealed plastic bucket or use the MDI Spill Kit. A used relay could release mercury. Mercury is very hazardous and must be handled properly. The unit(s) MUST be placed in a separate sealed container (plastic bucket with lid, or can with lid). At this point, please call MDI Inc. for specific hazardous material handling.
Any relays returned with out an RMA# will be refused.
11. What is MDI's warranty policy?
Mercury Displacement Industries, Inc. warranty's its products to be free from defects in our materials or workmanship for one year, and will fix or replace any units with such defects.
Warranty is void if units are improperly applied. Mercury Displacement Industries, Inc. shall not be liable for special or consequential damages.
We only offer a 90 day warranty on all resale items, which the manufacturer would have their own warranty.