and night (and a minimum of 10,000 watts at night, if grandfathered), certain existing Mexican Class A stations, and certain new Cuban Class A stations are authorized to operate at a higher power. Certain Mexican Class A stations are authorized to operate at less than 50,000 watts at night, if grandfathered, but may operate at up to 100,000 watts during the day. Class B and D stations can be found on any frequencies from 540 kHz to 1700 kHz except where frequencies have been reserved for Class C stations. Class C stations can be found in the lower 48 US states on the frequencies of 1230 kHz, 1240 kHz, 1340 kHz, 1400 kHz, 1450 kHz, and 1490 kHz (commonly known as "graveyard" frequencies). Other countries may use other frequencies for their Class C stations. American territories in ITU region 3 with AM broadcasting stations (Guam and the Northern Mariana Islands) use the 9 kHz spacing customary to the rest of the world. All stations are class B or lower. Canada also defines Class CC (Carrier Current, restricted to the premises) and LP. (less than 100 watts) TIS stations can be found on any frequency from 530 kHz to 1700 kHz in the US, but may only carry non-commercial messages without music. There is a network of TISs on 1710 in New Jersey. Low-power AM stations located on a school campus are allowed to be more powerful, so long as their signal strength does not exceed roughly 14 to 45 µV/m (microvolts per meter) (depending on frequency) at a distance of 30 meters (98.4 ft) from campus. Former system AM station classes were previously assigned Roman numerals from I to IV in the US, with subclasses indicated by a letter suffix. Current class A is equivalent to the old class I; class B is the old classes II and III, with class D being the II-D, II-S, and III-S subclasses; and class C is the old class IV. The following conversion table compares the old AM station classes with the new AM station classes: {| class="wikitable" |- ! Old Domestic Station Class ! New Domestic Station Class |- | I | A |- | II | B |- | III | B |- | IV | C |- | II-S | D |- | III-S | D |- | II-D(Daytime Only) | D |} AM station classes and clear channels listed